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Ab initio molecular orbital study of OH−(H2O)n and SH−(H2O)n in the gas phase
11 May 2001
Chemical Physics Letters 339 (2001) 279±289
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Ab initio molecular orbital study of OH H2On and SH H2On in the gas phase M. Masamura * Department of Preventive Dentistry, Okayama University Dental School, Shikata-cho 2-5-1, Okayama 700-8525, Japan Received 4 September 2000; in ®nal form 21 February 2001
Abstract This Letter is to show that the relative stability of several isomers of SH H2 On is considerably dierent from that of corresponding isomers of OH H2 On (n 3±5). Also, we clarify the cause for the dierence by energy decomposition. Ó 2001 Elsevier Science B.V. All rights reserved.
1. Introduction OH is a signi®cant substance because of its involvement in acid±base chemistry. For OH H2 On in the gas phase, many theoretical and experimental studies have been performed [1± 18]. Recently, we studied the relative stability of several isomers of OH H2 On (n 3±5) using MP2/aug-cc-pVDZ and MP4/aug-cc-pVDZ//MP2/ aug-cc-pVDZ methods [18]. Also, SH is a biologically important substance. For example, SH is poisonous. Thus, the relative stability of several isomers of SH H2 On (n 3±5) is interesting. For SH H2 On (n 1), ab initio molecular orbital studies have been carried out [19,20]. However, for SH H2 On n P 2, ab initio molecular orbital study has not yet been performed. The purpose of this Letter is to (1) show that the relative stability of several isomers of
*
Corresponding author. Fax: +81-86-235-6714. E-mail address: [email protected] (M. Masamura).
SH H2 On is considerably dierent from that of corresponding isomers of OH H2 On (n 3±5) and (2) clarify the cause for the dierence by means of energy decomposition [21]. This study suggests that it is quite possible that the relative stability of isomers of one anion with water molecules is dierent from that of other anions with water molecules in the gas phase. 2. Computational details We used the GA U S S I A N 94 [22] and GA U S S I A N 98 [23] programs, on the SX-5 and VPP 5000 computers at the Institute for Molecular Science. For F H2 On (n 3±5), several stationary points corresponding to dierent hydrogen bonding networks were considered in order to ensure adequate sampling of the multidimensional potential-energy surface [24]. For SH H2 On (n 3±5), we consider several isomers (Fig. 1) by reference to that study. Also, according to [25], we consider the `3-1(3)' and `4-1(3)' isomers. The 3-1(3) isomer has three water molecules in the ®rst solvent shell and one water molecule in the second solvent shell. The
0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 ( 0 1 ) 0 0 2 6 2 - 7
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M. Masamura / Chemical Physics Letters 339 (2001) 279±289
Fig. 1. The structures of SH H2 On (n 3±5) clusters in the gas phase.
4-1(3) isomer has four water molecules in the ®rst solvent shell and one water molecule in the second solvent shell. In the isomers, two hydrogen units of the water molecule in the second solvent shell interact with two oxygen units of the water molecules in the ®rst solvent shell, and one oxygen unit of the water molecule in the second solvent shell interacts with one hydrogen unit of the water molecule in the ®rst solvent shell. MP2/aug-ccpVDZ calculations cannot be carried out due to the large amount of CPU time necessary. We
carried out full geometry optimizations using MP2/6-31++G(2d,2p) method for SH H2 On n 3; 4. For SH H2 On n 5, full geometry optimizations cannot be performed due to the limitation of programs. Therefore, we also carried out full geometry optimizations using MP2/ 6-31++G(d,p) method for SH H2 On (n 3±5). We also performed vibrational analysis for all clusters at the optimized structures to con®rm that all vibrational frequencies are real. Also, we calculated the energies of those isomers at the
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
MP4SDTQ/6-311++G(2d,2p)//MP2/6-31++G(d,p) and MP4SDTQ/6-311++G(2d,2p)//MP2/6-31++G (2d,2p) levels. For MP4SDTQ/6-311++G(2d,2p)// MP2/6-31++G(d,p) calculations, zero-point energies were evaluated at the MP2/6-31++G(d,p) level. For the MP4SDTQ/6-311++G(2d,2p)//MP2/ 6-31++G(2d,2p) calculations, zero-point energies were evaluated at the MP2/6-31++G(2d,2p) level. The core electrons were frozen. For the reason described in [18], the keyword `VeryTight' in the GA U S S I A N 94 and GA U S S I A N 98 were not used.
281
That is to say, standard optimization convergence criteria were used. For OH H2 On (n 3±5) (Fig. 2), in [18], similar calculations were performed using MP2/ aug-cc-pVDZ and MP4SDTQ/aug-cc-pVDZ// MP2/aug-cc-pVDZ methods. Zero-point energies were evaluated using the MP2/aug-cc-pVDZ results. In addition, in this study, the 3-1(3) isomer was calculated using MP2/aug-cc-pVDZ and MP4SDTQ/aug-cc-pVDZ//MP2/aug-cc-pVDZ methods. The 4-1(3) isomer was not calculated
Fig. 2. The structures of OH H2 On (n 3±5) clusters in the gas phase.
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M. Masamura / Chemical Physics Letters 339 (2001) 279±289
because in SH H2 On n 5, the 4-1(3) structure collapsed to the `4-1(2)' isomer during the optimization. In this study, for OH H2 On and SH H2 On (n 3±5), energy decomposition calculations [21] were performed. The energy of each isomer was decomposed in terms of relaxation, 2-, 3- and 4-body interactions. 3. Results and discussion All the present clusters except for the `4-1(3)' structure have all real vibrational frequencies and correspond to equilibrium structures. As noted earlier, the `4-1(3)' isomer collapsed to the `4-1(2)' one during the optimization. Table 1 shows the energies for OH H2 On and SH H2 On .
Table 2 shows that (1) for n 3, the C3 symmetry is more stable than `2-1(2)', (2) for n 4, the stability of C4 symmetry is equal to that of `3-1(2)', 3-1(3) is less stable than C4 symmetry and 3-1(2), and `3-1(1)' is less stable than 3-1(3), and (3) for n 5, the stability of C5 symmetry is equal to that of `4-1(1)', and 4-1(2) is more stable than C5 symmetry and 4-1(1) by 2 kcal/mol. Table 3 shows that (1) for n 3, C3 symmetry is less stable than 2-1(2), (2) for n 4, C4 symmetry is more stable than 3-1(2), 3-1(1) and 3-1(3) are less stable than 3-1(2), and the stability of 3-1(1) is close to that of 3-1(3), and (3) for n 5, C5 symmetry is more stable than 4-1(1) and 4-1(2), and the stablity of 4-1(1) is close to that of 4-1(2). For F H2 On (n 4), 3-1(3) is most stable isomer [25]. However, for OH H2 On (n 4), the stability of 3-1(3) is the third. For SH H2 On (n 4), 3-1(3) is most unstable isomer.
Table 1 The energies for OH H2 On and SH H2 On (n 3±5) clusters (in Eh) n
MP4/aug-cc-pVDZ
C3 symmetry 2-1 (1)
)304.52823 )304.52638
)304.58060 )304.57838
4
C4 symmetry 3-1 (1) 3-1 (2) 3-1 (3)
)380.81748 )380.81042 )380.81749 )380.81351
)380.88395 )380.87615 )380.88365 )380.87961
5
C5 symmetry 4-1 (1) 4-1 (2)
)457.09753 )457.09766 )457.10075
)457.17810 )457.17771 )457.18103
MP2/6-31++G(d,p)
MP2/ 6-31++G(2d,2p)
MP4/ 6-311++G(2d,2p)a
MP4/ 6-311++G(2d,2p)b
C3 symmetry 2-1 (1)
)627.01254 )627.01701
)627.12745 )627.13139
)627.31767 )627.32133
)627.31794 )627.32203
4
C4 symmetry 3-1 (1) 3-1 (2) 3-1 (3)
)703.27580 )703.27004 )703.27407 )703.27013
)703.41993 )703.41325 )703.41746 )703.41378
)703.65543 )703.64873 )703.65309 )703.64955
)703.65617 )703.64947 )703.65402 )703.65044
5
C5 symmetry 4-1 (1) 4-1 (2)
)779.53139 )779.52758 )779.52835
SH H2 On 3
b
Energy MP2/aug-cc-pVDZ
OH H2 On 3
a
Isomer
MP2/6-31++G(d,p) geometries. MP2/6-31++G(2d,2p) geometries.
)779.98459 )779.98112 )779.98180
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
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Table 2 Relative stability of several isomers for OH H2 On (n 3±5) clusters (in kcal/mol)a Relative energy
n
Isomer
3
C3 symmetry 2-1 (1)
0.0 (0.0) 1.2 (0.7)
0.0 (0.0) 1.4 (0.9)
4
C4 symmetry 3-1 (1) 3-1 (2) 3-1 (3)
0.0 4.4 0.0 2.5
0.0 4.9 0.2 2.7
5
C5 symmetry 4-1 (1) 4-1 (2)
MP2/aug-cc-pVDZ
a
MP4/aug-cc-pVDZ
(0.0) (2.8) ()0.3) (1.6)
0.0 (0.0) )0.1 ()0.2) )2.0 ()0.9)
(0.0) (3.2) ()0.1) (1.8)
0.0 (0.0) 0.2 (0.1) )1.8 ()1.7)
Parentheses are relative energy including zero-point energy.
In brief, n 3 OH H2 O3 SH H2 O3 n 4 OH H2 O4 SH H2 O4 n 5 OH H2 O5 SH H2 O5
The OH ion starts with highly symmetric Cn structures with small degree of H-bonding between water molecules n 3; 4 and progresses to asymmetric ones with water in the second solvation shell for n 5 whereas the trend is opposite for SH which starts with structures exhibiting stronger H-bonding between water molecules (2-1(1) isomer for n 3) and progresses to isomers with higher symmetry and less inter-water H-bonding (Cn isomers for n 4; 5). The n 4 cluster seems to be the `turning point' for both since for this cluster size the C4 and 3-1(2) isomers are close in energy.
C3 > 2-1 2 more stable > less stable C3 < 2-1 2 C4 3-1 2 > 3-1 3 > 3-1 1 C4 > 3-1 2 > 3-1 3 ; 3-1 1 C5 4-1 1 < 4-1 2 C5 > 4-1 1 ; 4-1 2
Table 3 Relative stability of several isomers for SH H2 On (n 3±5) clusters (in kcal/mol)a n
a
Isomer
Relative energy MP2/ 6-31++G(d,p)
MP2/ 6-31++G(2d,2p)
MP4/ 6-311++G(2d,2p)b
MP4/ 6-311++G(2d,2p)c
0.0 (0.0) )2.8 ()1.2)
0.0 (0.0) )2.5 ()1.0)
0.0 (0.0) )2.3 ()0.8)
0.0 (0.0) )2.6 ()1.1)
3
C3 symmetry 2-1 (1)
4
C4 symmetry 3-1 (1) 3-1 (2) 3-1 (3)
0.0 3.6 1.1 3.6
5
C5 symmetry 4-1 (1) 4-1 (2)
0.0 (0.0) 2.4 (1.7) 1.9 (1.5)
(0.0) (2.4) (1.0) (2.7)
Parentheses are relative energy including zero-point energy. MP2/6-31++G(d,p) geometries. c MP2/6-31++G(2d,2p) geometries. b
0.0 4.2 1.6 3.9
(0.0) (2.5) (0.9) (2.5)
0.0 4.2 1.5 3.7
(0.0) (3.0) (1.4) (2.9)
0.0 (0.0) 2.2 (1.5) 1.8 (1.3)
0.0 4.2 1.4 3.6
(0.0) (2.5) (0.7) (2.2)
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For the relative stability of isomers of OH H2 On , Table 2 shows that MP2/aug-ccpVDZ results are close to the MP4/aug-cc-pVDZ// MP2/aug-cc-pVDZ results. Therefore, we performed the energy decomposition calculations at the MP2/aug-cc-pVDZ level. Table 4 shows the decomposition of the interaction energies for the isomers of OH H2 On . For n 3, the relaxation energy of C3 (3.2 kcal/ mol) is less positive than that of 2-1(2) (6.4 kcal/ mol). The 2-body interaction energy of C3 ( 78:6 kcal=mol) is more negative than that of 2-1(2) 76:0 kcal=mol. The 3-body interaction energy of C3 (7.3 kcal/mol) is more positive than that of 2-1(2) (2.0 kcal/mol). The 4-body interaction energy of C3 ( 0:1 kcal=mol is less positive
than that of 2-1(2) (0.7 kcal/mol). As a result, C3 symmetry is more stable than 2-1(2). For n 4, the relaxation energy of C4 (2.9 kcal/ mol) is less positive than that of 3-1(2) (4.2 kcal/mol), 3-1(3) (4.7 kcal/mol) and 3-1(1) (4.2 kcal/mol). The relaxation energies of 3-1(2), 3-1(3) and 3-1(1) are almost the same values. The 2-body interaction energy of C4 ( 101:0 kcal=mol is more negative than that of 3-1(2) ( 98:4 kcal= mol. The 2-body interaction energy of 3-1(2) is more negative than that of 3-1(3) 96:8 kcal= mol. The 2-body interaction energy of 3-1(3) is considerably more negative than that of 3-1(1) 90:8 kcal=mol. The 3-body interaction energy of C4 (13.1 kcal/mol) is considerably more positive than that of 3-1(2) (8.1 kcal/mol) and 3-1(3)
Table 4 Decomposition of the interaction energies for the isomers of OH H2 On (n 3±5) clusters at the MP2/aug-cc-pVDZ level (in kcal/ mol) n
Isomers
Relaxation
3
C3 symmetry
3.2
)78.6
2-1 (2)
6.4
)76.0
C4 symmetry
2.9
)101.0
3-1 (1)
4.2
)90.8
3-1 (2)
4.2
)98.4
3-1 (3)
4.7
)96.8
C5 symmetry
2.3
)118.1
4-1 (1)
3.4
)111.4
4-1 (2)
3.2
)117.0
4
5
a b
(Ion±water±water) 3-body term. (Water±water±water) 3-body term.
Total 2-body
Total 3-body
Total 4-body
Interaction energy
7.3 7.7a )0.4b 2.0 0.9 1.1
)0.1
)68.1
0.7
)66.9
13.1 14.1 )1.4 5.7 5.9 )0.2 8.1 8.5 )0.4 8.8 8.5 0.3
)1.0
)85.9
)0.7
)81.4
0.1
)85.9
)0.2
)83.4
)1.9
)97.9
)1.8
)98.0
)1.2
)99.9
19.3 21.6 )2.3 11.4 12.4 )1.0 14.7 15.6 )0.9
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
(8.8 kcal/mol). The 3-body interaction energy of 3-1(2) is close to that of 3-1(3). The 3-body interaction energy in 3-1(2) and 3-1(3) is more positive than that in 3-1(1) (5.7 kcal/mol). Therefore, as a result, the stability of C4 symmetry is equal to that of 3-1(2), 3-1(3) is less stable than C4 symmetry and 3-1(2), and 3-1(1) is less stable than 3-1(3). For n 5, the 2-body interaction energy of C5 ( 118:1 kcal=mol) is more negative than that of 4-1(2) 117:0 kcal=mol. The 3-body interaction energy of C5 (19.3 kcal/mol) is considerably more positive than that of 4-1(2) (14.7 kcal/mol). Therefore, as a result, C5 symmetry is less stable than 4-1(2). C5 < 4-1 2:
1
The 2-body interaction energy of C5 ( 118:1 kcal=mol) is considerably more negative than that of 4-1(1) 111:4 kcal=mol. The 3-body interaction energy of C5 (19.3 kcal/mol) is considerably more positive than that of 4-1(1) (11.4 kcal/mol). Therefore, as a result, the stability of C5 symmetry is equal to that of 4-1(1). C5 4-1 1:
2
From (1) and (2), C5 4-1 1 < 4-1 2. For the relative stability of isomers of SH H2 On , Table 3 shows that MP2/6-31++G(d, p) and MP2/6-31++G(2d,2p) results are close to MP4/6-311++G(2d,2p)//MP2/6-31++G(d, p) and MP4/6-311++G(2d,2p)//MP2/6-31++G(2d,2p) results. Therefore, we performed the energy decomposition calculations for MP2/6-31++G (d,p) and MP2/6-31++G(2d,2p) levels. Table 5 shows the decomposition of the interaction energies for the isomers of SH H2 On . For n 3, the 2-body interaction energy of C3 ( 47:8 in MP2/6-31++G(d,p); 45:8 kcal=mol in MP2/6-31++G(2d,2p)) is slightly less negative than that of 2-1(2) ( 48:5; 45:8 kcal=mol). The 3-body interaction energy of C3 (2.1; 2.8 kcal/mol) is more positive than that of 2-1(2) ( 0:3; 0:4 kcal=mol). As a result, C3 symmetry is less stable than 2-1(2). For n 4, the 2-body interaction energy of C4 ( 67:1; 62:5 kcal=mol) is considerably more negative than that of 3-1(2) ( 64:4; 60.6 kcal/mol).
285
The 2-body interaction energy of 3-1(2) is considerably more negative than that of 3-1(1) ( 60:9; 56.9 kcal/mol). The 3-body interaction energy of C4 (2.2; 1.1 kcal/mol) is more positive than that of 3-1(2) (0.8; 0.5 kcal/mol). The 3-body interaction energy of 3-1(2) is more positive than that of 3-1(1) ( 0:2; 0:4 kcal=mol). Therefore, as a result, C4 symmetry is more stable than 3-1(2), 3-1(1) is less stable than 3-1(2). C4 > 3
1 2 > 3
1 1:
3
The 2-body interaction energy of 3-1(1) ( 60:9; 56:9 kcal=mol) is less negative than that of 3-1(3) ( 62:6; 58:8 kcal=mol). The 3-body interaction energy of 3-1(1) ( 0:2; 0:4 kcal=mol) is less positive than that of 3-1(3) (1.4; 1.1 kcal/mol). As a result, the stability of 3-1(3) is close to that of 3-1(1). 3
1 3 ; 3
1 1:
4
From (3) and (4), C4 > 3 1 2 > 3 1 3 ; 3 1 1. For n 5, the 2-body interaction energy of C5 ( 83:3 kcal=mol) is considerably more negative than that of 4-1(2) 79:6 kcal=mol. The 3body interaction energy of C5 (4.1 kcal/mol) is more positive than that of 4-1(2) (2.4 kcal/mol). The 4-body interaction energy of C5 ( 0:6 kcal=mol) is more negative than that of 4-1(2) (0.6 kcal/mol). Therefore, as a result, C5 symmetry is more stable than 4-1(2). C5 > 4
1 2:
5
The 2-body interaction energy of 4-1(2) 79:6 kcal=mol is considerably more negative than that of 4-1(1) 76:9 kcal=mol. The 3-body interaction energy of 4-1(2) (2.4 kcal/mol) is considerably more positive than that of 4-1(1) (0.4 kcal/mol). As a result, the stability of 4-1(2) is close to that of 4-1(1). 4
1 2 ; 4
1 1:
6
From (5) and (6), C5 > 4 1 2 ; 4 1 1. From Table 5 most of the energetic dierence between the isomers for SH H2 O3 can be attributed to changes in the 3-body energies. For SH H2 O4 , most of the energetic dierence between the isomers can be attributed to changes in the 2-body and 3-body energies. For SH H2 O5 ,
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M. Masamura / Chemical Physics Letters 339 (2001) 279±289
Table 5 Decomposition of the interaction energies for the isomers of SH H2 On (n 3±5) clusters at the MP2/6-31++G(d,p) and MP2/ 6-31++G(2d,2p) levels (in kcal/mol) n
Isomers
Relaxation
Total 2-body
Total 3-body
3
C3 symmetry
1.1a
)47.8
1.3d
)45.8
1.2
)48.5
1.5
)45.8
2.1 2.1b 0.0c 2.8 2.9 0.0 )0.3 )1.1 0.8 )0.4 )1.3 0.9
1.3
)67.1
1.5
)62.5
1.4
)60.9
1.6
)56.9
1.1
)64.4
1.5
)60.6
1.2
)62.6
1.4
)58.8
C5 symmetry
1.7
)83.3
4-1 (1)
1.6
)76.9
4-1 (2)
1.4
)79.6
2-1 (2)
4
C4 symmetry
3-1 (1)
3-1 (2)
3-1 (3)
5
a
MP2/6-31++G(d,p) results. (Ion±water±water) 3-body term. c (Water±water±water) 3-body term. d MP2/6-31++G(2d,2p) results. b
Total 4-body
Interaction energy
0.1
)44.5
)0.1
)41.9
0.3
)47.3
0.4
)44.4
2.2 4.2 )2.0 1.1 4.0 )2.9 )0.2 0.6 )0.8 )0.4 0.5 )0.9 0.8 1.9 )1.1 0.5 1.8 )1.3 1.4 1.5 )0.1 1.1 1.3 )0.2
)0.1
)63.2
)0.1
)59.9
0.1
)59.6
)0.1
)55.7
0.4
)62.1
0.4
)58.4
0.4
)59.6
0.2
)56.0
4.1 6.8 )2.7 0.4 2.6 )2.2 2.4 3.5 )1.1
)0.6
)77.1
)0.2
)74.8
0.6
)75.2
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
most of the energetic dierence between the isomers can be attributed to changes in the 2-body energies. From Table 4 (ion±water±water) 3-body term is responsible for the energy dierence between the
287
various isomers for OH H2 On . From Table 5 (ion±water±water) and (water±water±water) 3-body terms are responsible for the energy difference between the various isomers for SH H2 On . From Tables 4 and 5 (ion±water±
Table 6 between neighboring water molecules and (water±water±water) 3-body term (in kcal/mol) The intermolecular O±O distances (in A) Isomer C3 2-1 (2) C4
3-1 (1) 3-1 (2)
3-1 (3)
C5
4-1 (1)
4-1 (2)
a
Atom±atoma
OH
SH
4-7 4-10 7-10 4-10 7-10
3.32b 3.32 3.32 2.91 2.91
)0.4c
4-10 4-13 7-10 7-13 4-7 4-10 7-10 4-7 4-9 4-13 7-9 7-13 4-9 4-13 7-9 7-13 9-13
3.13 3.13 3.13 3.13 3.21 4.28 3.39 4.19 2.91 3.45 2.90 3.43 2.94 3.81 2.94 3.81 3.13
)1.4
4-7 4-16 7-10 10-13 13-16 4-10 4-13 7-10 7-13 4-9 4-13 4-16 7-9 7-13 7-16
3.05 3.05 3.05 3.05 3.05 3.04 3.21 3.11 3.11 2.94 3.35 3.20 2.92 3.26 4.18
)2.3
1.1
)0.2 )0.4
0.3
)1.0
)0.9
5.48d 5.48 5.48 2.94 2.94
5.56e 5.56 5.56 2.93 2.93
2.95 2.95 2.95 2.95 2.94 4.91 3.02 4.49 2.93 4.56 2.92 3.06 2.93 4.56 2.92 3.06 2.97
2.89 2.89 2.89 2.89 2.92 4.85 3.02 4.33 2.89 4.53 2.89 3.04 2.88 3.70 2.88 3.70 2.96
2.95 2.95 2.95 2.95 2.95 2.89 3.02 2.93 2.92 2.93 3.71 3.05 2.95 3.09 5.70
See Figs. 1 and 2. O±O distance obtained using MP2/aug-cc-pVDZ. c (Water±water±water) 3-body term obtained using MP2/aug-cc-pVDZ. d O±O distance obtained using MP2/6-31++G(d,p). e O±O distance obtained using MP2/6-31++G(2d,2p). f (Water-water-water) 3-body term obtained using MP2/6-31++G(d,p). g (Water-water-water) 3-body term obtained using MP2/6-31++G(2d,2p). b
0.0f
0.0g
0.8
0.9
)2.0
)2.9
)0.8
)0.9
)1.1
)1.3
)0.1
)0.2
)2.7
)2.2
)1.1
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M. Masamura / Chemical Physics Letters 339 (2001) 279±289
water) 3-body term is responsible for the energy dierence between the isomers for OH H2 On and the corresponding isomers for SH H2 On . The fact that the SH ion should be larger than the OH one should aect the hydrogen bonding network between the water molecules and have them bound `more tightly' to each other for the case of SH H2 On than for OH H2 On where the ion±water interaction is stronger. Such a fact should re¯ect a stronger (water±water±water) 3-body term for SH H2 On than for OH H2 On . Table 6 shows that this is valid, except for the C3 isomers for the following fact (A). From Table 6 larger (water±water±water) 3-body term for the isomers for SH H2 On is associated with smaller O-O separations between neighboring water molecules than for the corresponding isomers for OH H2 On , except for the C3 , 3-1(2) and 4-1(2) isomers. In the C3 isomers, the larger (water-waterwater) 3-body term for OH H2 O3 is associated with smaller O-O separations between neighboring water molecules than for SH H2 O3 (fact (A)). Fully optimized structural parameters are available from the author (at no charge).
4. Conclusions (1) The relative stability of several isomers of SH H2 On is considerably dierent from that of corresponding isomers of OH H2 On (n 3±5): In OH H2 O3 ; C3 > 2 1 2; in SH H2 O3 ; C3 < 2 1 2. In OH H2 O4 ; C4 3 1 2 > 3 1 3 > 3 1 1; in SH H2 O4 ; C4 > 3 1 2 > 3 1 3 ; 3 1 1. In OH H2 O5 ; C5 4 1 1 < 4 1 2; in SH H2 O5 ; C5 > 4 1 1 ; 4 1 2. The OH ion starts with highly symmetric Cn structures with small degree of Hbonding between water molecules (n 3; 4) and progresses to asymmetric ones with water in the second solvation shell for n 5 whereas the trend is opposite for SH which starts with structures exhibiting stronger H-bonding between water molecules (2-1(1) isomer for n 3) and progresses to isomers with higher symmetry and less interwater H-bonding (Cn isomers for n 4; 5). The
n 4 cluster seems to be the turning point for both since for this cluster size the C4 and 3-1(2) isomers are close in energy. (2) We clarify the cause for the dierence by energy decomposition. Acknowledgements We are grateful to the Institute for Molecular Science for the use of computer time and the GA U S S I A N 94 and GA U S S I A N 98 programs. References [1] M. Arshadi, P. Kebarle, J. Phys. Chem. 74 (1970) 1483. [2] M.D. Newton, S. Ehrenson, J. Am. Chem. Soc. 93 (1971) 4971. [3] A.-M. Sapse, L. Osorio, G. Snyder, Int. J. Quantum Chem. 26 (1984) 223. [4] M. Meot-Ner (Mautner), J. Am. Chem. Soc. 108 (1986) 6189. [5] M. Meot-Ner (Mautner), C.V. Speller, J. Phys. Chem. 90 (1986) 6616. [6] J.D. Madura, W.L. Jorgensen, J. Am.Chem. Soc. 108 (1986) 2517. [7] G. Andaloro, M.A. Palazzo, M. Migliore, S.L. Fornnili, Chem. Phys. Lett. 201 (1988) 149. [8] M. Tuckerman, K. Lassonen, M. Sprik, M. Parrinello, J. Phys.: Condens. Matter 6 (1994) 93. [9] I. Tunon, D. Rinaldi, M.F. Ruiz-Lopez, J.L. Rivail, J. Phys. Chem. 99 (1995) 3798. [10] S.S. Xantheas, J. Am. Chem. Soc. 117 (1995) 10379. [11] A.R. Grimm, G.B. Bacskay, A.D. Haymet, Mol. Phys. 86 (1995) 369. [12] M. Tuckerman, K. Lassonen, M. Sprik, M. Parrinello, J. Chem. Phys. 103 (1995) 150. [13] M. Tuckerman, K. Lassonen, M. Sprik, M. Parrinello, J. Phys. Chem. 99 (1995) 5749. [14] M. Tuckerman, M. Sprik, M. Parrinello, Femtochemistry (1996) 578. [15] C.P. Del Valle, J.J. Novoa, Chem. Phys. Lett. 269 (1997) 401. [16] J.J. Novoa, F. Mota, C.P. Del Valle, M. Planas, J. Phys. Chem. A 101 (1997) 7842. [17] M. Masamura, J. Mol. Struct. (Theochem) 498 (2000) 87. [18] M. Masamura, J. Comput. Chem. 22 (2001) 31. [19] J. Gao, D.S. Garner, W.L. Jorgensen, J. Am. Chem. Soc. 108 (1986) 4784. [20] J.E. Del Bene, J. Phys. Chem. 92 (1988) 2874. [21] S.S. Xantheas, J. Chem. Phys. 100 (1994) 7523.
M. Masamura / Chemical Physics Letters 339 (2001) 279±289 [22] M.J. Frisch et al., Gaussian Inc., Pittsburgh, PA, 1995. [23] M.J. Frisch et al., Gaussian Inc., Pittsburgh, PA, 1998. [24] O.M. Cabarcos, C.J. Weinheimer, J.M. Lisy, S.S. Xantheas, J. Chem. Phys. 110 (1999) 5.
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[25] S.J. Vaughen, E.V. Akhmatskaya, M.A. Vincent, A.J. Masters, I.H. Hiller, J. Chem. Phys. 110 (1999) 4338.
Chemical Physics Letters 339 (2001) 279±289
www.elsevier.nl/locate/cplett
Ab initio molecular orbital study of OH H2On and SH H2On in the gas phase M. Masamura * Department of Preventive Dentistry, Okayama University Dental School, Shikata-cho 2-5-1, Okayama 700-8525, Japan Received 4 September 2000; in ®nal form 21 February 2001
Abstract This Letter is to show that the relative stability of several isomers of SH H2 On is considerably dierent from that of corresponding isomers of OH H2 On (n 3±5). Also, we clarify the cause for the dierence by energy decomposition. Ó 2001 Elsevier Science B.V. All rights reserved.
1. Introduction OH is a signi®cant substance because of its involvement in acid±base chemistry. For OH H2 On in the gas phase, many theoretical and experimental studies have been performed [1± 18]. Recently, we studied the relative stability of several isomers of OH H2 On (n 3±5) using MP2/aug-cc-pVDZ and MP4/aug-cc-pVDZ//MP2/ aug-cc-pVDZ methods [18]. Also, SH is a biologically important substance. For example, SH is poisonous. Thus, the relative stability of several isomers of SH H2 On (n 3±5) is interesting. For SH H2 On (n 1), ab initio molecular orbital studies have been carried out [19,20]. However, for SH H2 On n P 2, ab initio molecular orbital study has not yet been performed. The purpose of this Letter is to (1) show that the relative stability of several isomers of
*
Corresponding author. Fax: +81-86-235-6714. E-mail address: [email protected] (M. Masamura).
SH H2 On is considerably dierent from that of corresponding isomers of OH H2 On (n 3±5) and (2) clarify the cause for the dierence by means of energy decomposition [21]. This study suggests that it is quite possible that the relative stability of isomers of one anion with water molecules is dierent from that of other anions with water molecules in the gas phase. 2. Computational details We used the GA U S S I A N 94 [22] and GA U S S I A N 98 [23] programs, on the SX-5 and VPP 5000 computers at the Institute for Molecular Science. For F H2 On (n 3±5), several stationary points corresponding to dierent hydrogen bonding networks were considered in order to ensure adequate sampling of the multidimensional potential-energy surface [24]. For SH H2 On (n 3±5), we consider several isomers (Fig. 1) by reference to that study. Also, according to [25], we consider the `3-1(3)' and `4-1(3)' isomers. The 3-1(3) isomer has three water molecules in the ®rst solvent shell and one water molecule in the second solvent shell. The
0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 ( 0 1 ) 0 0 2 6 2 - 7
280
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
Fig. 1. The structures of SH H2 On (n 3±5) clusters in the gas phase.
4-1(3) isomer has four water molecules in the ®rst solvent shell and one water molecule in the second solvent shell. In the isomers, two hydrogen units of the water molecule in the second solvent shell interact with two oxygen units of the water molecules in the ®rst solvent shell, and one oxygen unit of the water molecule in the second solvent shell interacts with one hydrogen unit of the water molecule in the ®rst solvent shell. MP2/aug-ccpVDZ calculations cannot be carried out due to the large amount of CPU time necessary. We
carried out full geometry optimizations using MP2/6-31++G(2d,2p) method for SH H2 On n 3; 4. For SH H2 On n 5, full geometry optimizations cannot be performed due to the limitation of programs. Therefore, we also carried out full geometry optimizations using MP2/ 6-31++G(d,p) method for SH H2 On (n 3±5). We also performed vibrational analysis for all clusters at the optimized structures to con®rm that all vibrational frequencies are real. Also, we calculated the energies of those isomers at the
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
MP4SDTQ/6-311++G(2d,2p)//MP2/6-31++G(d,p) and MP4SDTQ/6-311++G(2d,2p)//MP2/6-31++G (2d,2p) levels. For MP4SDTQ/6-311++G(2d,2p)// MP2/6-31++G(d,p) calculations, zero-point energies were evaluated at the MP2/6-31++G(d,p) level. For the MP4SDTQ/6-311++G(2d,2p)//MP2/ 6-31++G(2d,2p) calculations, zero-point energies were evaluated at the MP2/6-31++G(2d,2p) level. The core electrons were frozen. For the reason described in [18], the keyword `VeryTight' in the GA U S S I A N 94 and GA U S S I A N 98 were not used.
281
That is to say, standard optimization convergence criteria were used. For OH H2 On (n 3±5) (Fig. 2), in [18], similar calculations were performed using MP2/ aug-cc-pVDZ and MP4SDTQ/aug-cc-pVDZ// MP2/aug-cc-pVDZ methods. Zero-point energies were evaluated using the MP2/aug-cc-pVDZ results. In addition, in this study, the 3-1(3) isomer was calculated using MP2/aug-cc-pVDZ and MP4SDTQ/aug-cc-pVDZ//MP2/aug-cc-pVDZ methods. The 4-1(3) isomer was not calculated
Fig. 2. The structures of OH H2 On (n 3±5) clusters in the gas phase.
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M. Masamura / Chemical Physics Letters 339 (2001) 279±289
because in SH H2 On n 5, the 4-1(3) structure collapsed to the `4-1(2)' isomer during the optimization. In this study, for OH H2 On and SH H2 On (n 3±5), energy decomposition calculations [21] were performed. The energy of each isomer was decomposed in terms of relaxation, 2-, 3- and 4-body interactions. 3. Results and discussion All the present clusters except for the `4-1(3)' structure have all real vibrational frequencies and correspond to equilibrium structures. As noted earlier, the `4-1(3)' isomer collapsed to the `4-1(2)' one during the optimization. Table 1 shows the energies for OH H2 On and SH H2 On .
Table 2 shows that (1) for n 3, the C3 symmetry is more stable than `2-1(2)', (2) for n 4, the stability of C4 symmetry is equal to that of `3-1(2)', 3-1(3) is less stable than C4 symmetry and 3-1(2), and `3-1(1)' is less stable than 3-1(3), and (3) for n 5, the stability of C5 symmetry is equal to that of `4-1(1)', and 4-1(2) is more stable than C5 symmetry and 4-1(1) by 2 kcal/mol. Table 3 shows that (1) for n 3, C3 symmetry is less stable than 2-1(2), (2) for n 4, C4 symmetry is more stable than 3-1(2), 3-1(1) and 3-1(3) are less stable than 3-1(2), and the stability of 3-1(1) is close to that of 3-1(3), and (3) for n 5, C5 symmetry is more stable than 4-1(1) and 4-1(2), and the stablity of 4-1(1) is close to that of 4-1(2). For F H2 On (n 4), 3-1(3) is most stable isomer [25]. However, for OH H2 On (n 4), the stability of 3-1(3) is the third. For SH H2 On (n 4), 3-1(3) is most unstable isomer.
Table 1 The energies for OH H2 On and SH H2 On (n 3±5) clusters (in Eh) n
MP4/aug-cc-pVDZ
C3 symmetry 2-1 (1)
)304.52823 )304.52638
)304.58060 )304.57838
4
C4 symmetry 3-1 (1) 3-1 (2) 3-1 (3)
)380.81748 )380.81042 )380.81749 )380.81351
)380.88395 )380.87615 )380.88365 )380.87961
5
C5 symmetry 4-1 (1) 4-1 (2)
)457.09753 )457.09766 )457.10075
)457.17810 )457.17771 )457.18103
MP2/6-31++G(d,p)
MP2/ 6-31++G(2d,2p)
MP4/ 6-311++G(2d,2p)a
MP4/ 6-311++G(2d,2p)b
C3 symmetry 2-1 (1)
)627.01254 )627.01701
)627.12745 )627.13139
)627.31767 )627.32133
)627.31794 )627.32203
4
C4 symmetry 3-1 (1) 3-1 (2) 3-1 (3)
)703.27580 )703.27004 )703.27407 )703.27013
)703.41993 )703.41325 )703.41746 )703.41378
)703.65543 )703.64873 )703.65309 )703.64955
)703.65617 )703.64947 )703.65402 )703.65044
5
C5 symmetry 4-1 (1) 4-1 (2)
)779.53139 )779.52758 )779.52835
SH H2 On 3
b
Energy MP2/aug-cc-pVDZ
OH H2 On 3
a
Isomer
MP2/6-31++G(d,p) geometries. MP2/6-31++G(2d,2p) geometries.
)779.98459 )779.98112 )779.98180
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
283
Table 2 Relative stability of several isomers for OH H2 On (n 3±5) clusters (in kcal/mol)a Relative energy
n
Isomer
3
C3 symmetry 2-1 (1)
0.0 (0.0) 1.2 (0.7)
0.0 (0.0) 1.4 (0.9)
4
C4 symmetry 3-1 (1) 3-1 (2) 3-1 (3)
0.0 4.4 0.0 2.5
0.0 4.9 0.2 2.7
5
C5 symmetry 4-1 (1) 4-1 (2)
MP2/aug-cc-pVDZ
a
MP4/aug-cc-pVDZ
(0.0) (2.8) ()0.3) (1.6)
0.0 (0.0) )0.1 ()0.2) )2.0 ()0.9)
(0.0) (3.2) ()0.1) (1.8)
0.0 (0.0) 0.2 (0.1) )1.8 ()1.7)
Parentheses are relative energy including zero-point energy.
In brief, n 3 OH H2 O3 SH H2 O3 n 4 OH H2 O4 SH H2 O4 n 5 OH H2 O5 SH H2 O5
The OH ion starts with highly symmetric Cn structures with small degree of H-bonding between water molecules n 3; 4 and progresses to asymmetric ones with water in the second solvation shell for n 5 whereas the trend is opposite for SH which starts with structures exhibiting stronger H-bonding between water molecules (2-1(1) isomer for n 3) and progresses to isomers with higher symmetry and less inter-water H-bonding (Cn isomers for n 4; 5). The n 4 cluster seems to be the `turning point' for both since for this cluster size the C4 and 3-1(2) isomers are close in energy.
C3 > 2-1 2 more stable > less stable C3 < 2-1 2 C4 3-1 2 > 3-1 3 > 3-1 1 C4 > 3-1 2 > 3-1 3 ; 3-1 1 C5 4-1 1 < 4-1 2 C5 > 4-1 1 ; 4-1 2
Table 3 Relative stability of several isomers for SH H2 On (n 3±5) clusters (in kcal/mol)a n
a
Isomer
Relative energy MP2/ 6-31++G(d,p)
MP2/ 6-31++G(2d,2p)
MP4/ 6-311++G(2d,2p)b
MP4/ 6-311++G(2d,2p)c
0.0 (0.0) )2.8 ()1.2)
0.0 (0.0) )2.5 ()1.0)
0.0 (0.0) )2.3 ()0.8)
0.0 (0.0) )2.6 ()1.1)
3
C3 symmetry 2-1 (1)
4
C4 symmetry 3-1 (1) 3-1 (2) 3-1 (3)
0.0 3.6 1.1 3.6
5
C5 symmetry 4-1 (1) 4-1 (2)
0.0 (0.0) 2.4 (1.7) 1.9 (1.5)
(0.0) (2.4) (1.0) (2.7)
Parentheses are relative energy including zero-point energy. MP2/6-31++G(d,p) geometries. c MP2/6-31++G(2d,2p) geometries. b
0.0 4.2 1.6 3.9
(0.0) (2.5) (0.9) (2.5)
0.0 4.2 1.5 3.7
(0.0) (3.0) (1.4) (2.9)
0.0 (0.0) 2.2 (1.5) 1.8 (1.3)
0.0 4.2 1.4 3.6
(0.0) (2.5) (0.7) (2.2)
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M. Masamura / Chemical Physics Letters 339 (2001) 279±289
For the relative stability of isomers of OH H2 On , Table 2 shows that MP2/aug-ccpVDZ results are close to the MP4/aug-cc-pVDZ// MP2/aug-cc-pVDZ results. Therefore, we performed the energy decomposition calculations at the MP2/aug-cc-pVDZ level. Table 4 shows the decomposition of the interaction energies for the isomers of OH H2 On . For n 3, the relaxation energy of C3 (3.2 kcal/ mol) is less positive than that of 2-1(2) (6.4 kcal/ mol). The 2-body interaction energy of C3 ( 78:6 kcal=mol) is more negative than that of 2-1(2) 76:0 kcal=mol. The 3-body interaction energy of C3 (7.3 kcal/mol) is more positive than that of 2-1(2) (2.0 kcal/mol). The 4-body interaction energy of C3 ( 0:1 kcal=mol is less positive
than that of 2-1(2) (0.7 kcal/mol). As a result, C3 symmetry is more stable than 2-1(2). For n 4, the relaxation energy of C4 (2.9 kcal/ mol) is less positive than that of 3-1(2) (4.2 kcal/mol), 3-1(3) (4.7 kcal/mol) and 3-1(1) (4.2 kcal/mol). The relaxation energies of 3-1(2), 3-1(3) and 3-1(1) are almost the same values. The 2-body interaction energy of C4 ( 101:0 kcal=mol is more negative than that of 3-1(2) ( 98:4 kcal= mol. The 2-body interaction energy of 3-1(2) is more negative than that of 3-1(3) 96:8 kcal= mol. The 2-body interaction energy of 3-1(3) is considerably more negative than that of 3-1(1) 90:8 kcal=mol. The 3-body interaction energy of C4 (13.1 kcal/mol) is considerably more positive than that of 3-1(2) (8.1 kcal/mol) and 3-1(3)
Table 4 Decomposition of the interaction energies for the isomers of OH H2 On (n 3±5) clusters at the MP2/aug-cc-pVDZ level (in kcal/ mol) n
Isomers
Relaxation
3
C3 symmetry
3.2
)78.6
2-1 (2)
6.4
)76.0
C4 symmetry
2.9
)101.0
3-1 (1)
4.2
)90.8
3-1 (2)
4.2
)98.4
3-1 (3)
4.7
)96.8
C5 symmetry
2.3
)118.1
4-1 (1)
3.4
)111.4
4-1 (2)
3.2
)117.0
4
5
a b
(Ion±water±water) 3-body term. (Water±water±water) 3-body term.
Total 2-body
Total 3-body
Total 4-body
Interaction energy
7.3 7.7a )0.4b 2.0 0.9 1.1
)0.1
)68.1
0.7
)66.9
13.1 14.1 )1.4 5.7 5.9 )0.2 8.1 8.5 )0.4 8.8 8.5 0.3
)1.0
)85.9
)0.7
)81.4
0.1
)85.9
)0.2
)83.4
)1.9
)97.9
)1.8
)98.0
)1.2
)99.9
19.3 21.6 )2.3 11.4 12.4 )1.0 14.7 15.6 )0.9
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
(8.8 kcal/mol). The 3-body interaction energy of 3-1(2) is close to that of 3-1(3). The 3-body interaction energy in 3-1(2) and 3-1(3) is more positive than that in 3-1(1) (5.7 kcal/mol). Therefore, as a result, the stability of C4 symmetry is equal to that of 3-1(2), 3-1(3) is less stable than C4 symmetry and 3-1(2), and 3-1(1) is less stable than 3-1(3). For n 5, the 2-body interaction energy of C5 ( 118:1 kcal=mol) is more negative than that of 4-1(2) 117:0 kcal=mol. The 3-body interaction energy of C5 (19.3 kcal/mol) is considerably more positive than that of 4-1(2) (14.7 kcal/mol). Therefore, as a result, C5 symmetry is less stable than 4-1(2). C5 < 4-1 2:
1
The 2-body interaction energy of C5 ( 118:1 kcal=mol) is considerably more negative than that of 4-1(1) 111:4 kcal=mol. The 3-body interaction energy of C5 (19.3 kcal/mol) is considerably more positive than that of 4-1(1) (11.4 kcal/mol). Therefore, as a result, the stability of C5 symmetry is equal to that of 4-1(1). C5 4-1 1:
2
From (1) and (2), C5 4-1 1 < 4-1 2. For the relative stability of isomers of SH H2 On , Table 3 shows that MP2/6-31++G(d, p) and MP2/6-31++G(2d,2p) results are close to MP4/6-311++G(2d,2p)//MP2/6-31++G(d, p) and MP4/6-311++G(2d,2p)//MP2/6-31++G(2d,2p) results. Therefore, we performed the energy decomposition calculations for MP2/6-31++G (d,p) and MP2/6-31++G(2d,2p) levels. Table 5 shows the decomposition of the interaction energies for the isomers of SH H2 On . For n 3, the 2-body interaction energy of C3 ( 47:8 in MP2/6-31++G(d,p); 45:8 kcal=mol in MP2/6-31++G(2d,2p)) is slightly less negative than that of 2-1(2) ( 48:5; 45:8 kcal=mol). The 3-body interaction energy of C3 (2.1; 2.8 kcal/mol) is more positive than that of 2-1(2) ( 0:3; 0:4 kcal=mol). As a result, C3 symmetry is less stable than 2-1(2). For n 4, the 2-body interaction energy of C4 ( 67:1; 62:5 kcal=mol) is considerably more negative than that of 3-1(2) ( 64:4; 60.6 kcal/mol).
285
The 2-body interaction energy of 3-1(2) is considerably more negative than that of 3-1(1) ( 60:9; 56.9 kcal/mol). The 3-body interaction energy of C4 (2.2; 1.1 kcal/mol) is more positive than that of 3-1(2) (0.8; 0.5 kcal/mol). The 3-body interaction energy of 3-1(2) is more positive than that of 3-1(1) ( 0:2; 0:4 kcal=mol). Therefore, as a result, C4 symmetry is more stable than 3-1(2), 3-1(1) is less stable than 3-1(2). C4 > 3
1 2 > 3
1 1:
3
The 2-body interaction energy of 3-1(1) ( 60:9; 56:9 kcal=mol) is less negative than that of 3-1(3) ( 62:6; 58:8 kcal=mol). The 3-body interaction energy of 3-1(1) ( 0:2; 0:4 kcal=mol) is less positive than that of 3-1(3) (1.4; 1.1 kcal/mol). As a result, the stability of 3-1(3) is close to that of 3-1(1). 3
1 3 ; 3
1 1:
4
From (3) and (4), C4 > 3 1 2 > 3 1 3 ; 3 1 1. For n 5, the 2-body interaction energy of C5 ( 83:3 kcal=mol) is considerably more negative than that of 4-1(2) 79:6 kcal=mol. The 3body interaction energy of C5 (4.1 kcal/mol) is more positive than that of 4-1(2) (2.4 kcal/mol). The 4-body interaction energy of C5 ( 0:6 kcal=mol) is more negative than that of 4-1(2) (0.6 kcal/mol). Therefore, as a result, C5 symmetry is more stable than 4-1(2). C5 > 4
1 2:
5
The 2-body interaction energy of 4-1(2) 79:6 kcal=mol is considerably more negative than that of 4-1(1) 76:9 kcal=mol. The 3-body interaction energy of 4-1(2) (2.4 kcal/mol) is considerably more positive than that of 4-1(1) (0.4 kcal/mol). As a result, the stability of 4-1(2) is close to that of 4-1(1). 4
1 2 ; 4
1 1:
6
From (5) and (6), C5 > 4 1 2 ; 4 1 1. From Table 5 most of the energetic dierence between the isomers for SH H2 O3 can be attributed to changes in the 3-body energies. For SH H2 O4 , most of the energetic dierence between the isomers can be attributed to changes in the 2-body and 3-body energies. For SH H2 O5 ,
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M. Masamura / Chemical Physics Letters 339 (2001) 279±289
Table 5 Decomposition of the interaction energies for the isomers of SH H2 On (n 3±5) clusters at the MP2/6-31++G(d,p) and MP2/ 6-31++G(2d,2p) levels (in kcal/mol) n
Isomers
Relaxation
Total 2-body
Total 3-body
3
C3 symmetry
1.1a
)47.8
1.3d
)45.8
1.2
)48.5
1.5
)45.8
2.1 2.1b 0.0c 2.8 2.9 0.0 )0.3 )1.1 0.8 )0.4 )1.3 0.9
1.3
)67.1
1.5
)62.5
1.4
)60.9
1.6
)56.9
1.1
)64.4
1.5
)60.6
1.2
)62.6
1.4
)58.8
C5 symmetry
1.7
)83.3
4-1 (1)
1.6
)76.9
4-1 (2)
1.4
)79.6
2-1 (2)
4
C4 symmetry
3-1 (1)
3-1 (2)
3-1 (3)
5
a
MP2/6-31++G(d,p) results. (Ion±water±water) 3-body term. c (Water±water±water) 3-body term. d MP2/6-31++G(2d,2p) results. b
Total 4-body
Interaction energy
0.1
)44.5
)0.1
)41.9
0.3
)47.3
0.4
)44.4
2.2 4.2 )2.0 1.1 4.0 )2.9 )0.2 0.6 )0.8 )0.4 0.5 )0.9 0.8 1.9 )1.1 0.5 1.8 )1.3 1.4 1.5 )0.1 1.1 1.3 )0.2
)0.1
)63.2
)0.1
)59.9
0.1
)59.6
)0.1
)55.7
0.4
)62.1
0.4
)58.4
0.4
)59.6
0.2
)56.0
4.1 6.8 )2.7 0.4 2.6 )2.2 2.4 3.5 )1.1
)0.6
)77.1
)0.2
)74.8
0.6
)75.2
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
most of the energetic dierence between the isomers can be attributed to changes in the 2-body energies. From Table 4 (ion±water±water) 3-body term is responsible for the energy dierence between the
287
various isomers for OH H2 On . From Table 5 (ion±water±water) and (water±water±water) 3-body terms are responsible for the energy difference between the various isomers for SH H2 On . From Tables 4 and 5 (ion±water±
Table 6 between neighboring water molecules and (water±water±water) 3-body term (in kcal/mol) The intermolecular O±O distances (in A) Isomer C3 2-1 (2) C4
3-1 (1) 3-1 (2)
3-1 (3)
C5
4-1 (1)
4-1 (2)
a
Atom±atoma
OH
SH
4-7 4-10 7-10 4-10 7-10
3.32b 3.32 3.32 2.91 2.91
)0.4c
4-10 4-13 7-10 7-13 4-7 4-10 7-10 4-7 4-9 4-13 7-9 7-13 4-9 4-13 7-9 7-13 9-13
3.13 3.13 3.13 3.13 3.21 4.28 3.39 4.19 2.91 3.45 2.90 3.43 2.94 3.81 2.94 3.81 3.13
)1.4
4-7 4-16 7-10 10-13 13-16 4-10 4-13 7-10 7-13 4-9 4-13 4-16 7-9 7-13 7-16
3.05 3.05 3.05 3.05 3.05 3.04 3.21 3.11 3.11 2.94 3.35 3.20 2.92 3.26 4.18
)2.3
1.1
)0.2 )0.4
0.3
)1.0
)0.9
5.48d 5.48 5.48 2.94 2.94
5.56e 5.56 5.56 2.93 2.93
2.95 2.95 2.95 2.95 2.94 4.91 3.02 4.49 2.93 4.56 2.92 3.06 2.93 4.56 2.92 3.06 2.97
2.89 2.89 2.89 2.89 2.92 4.85 3.02 4.33 2.89 4.53 2.89 3.04 2.88 3.70 2.88 3.70 2.96
2.95 2.95 2.95 2.95 2.95 2.89 3.02 2.93 2.92 2.93 3.71 3.05 2.95 3.09 5.70
See Figs. 1 and 2. O±O distance obtained using MP2/aug-cc-pVDZ. c (Water±water±water) 3-body term obtained using MP2/aug-cc-pVDZ. d O±O distance obtained using MP2/6-31++G(d,p). e O±O distance obtained using MP2/6-31++G(2d,2p). f (Water-water-water) 3-body term obtained using MP2/6-31++G(d,p). g (Water-water-water) 3-body term obtained using MP2/6-31++G(2d,2p). b
0.0f
0.0g
0.8
0.9
)2.0
)2.9
)0.8
)0.9
)1.1
)1.3
)0.1
)0.2
)2.7
)2.2
)1.1
288
M. Masamura / Chemical Physics Letters 339 (2001) 279±289
water) 3-body term is responsible for the energy dierence between the isomers for OH H2 On and the corresponding isomers for SH H2 On . The fact that the SH ion should be larger than the OH one should aect the hydrogen bonding network between the water molecules and have them bound `more tightly' to each other for the case of SH H2 On than for OH H2 On where the ion±water interaction is stronger. Such a fact should re¯ect a stronger (water±water±water) 3-body term for SH H2 On than for OH H2 On . Table 6 shows that this is valid, except for the C3 isomers for the following fact (A). From Table 6 larger (water±water±water) 3-body term for the isomers for SH H2 On is associated with smaller O-O separations between neighboring water molecules than for the corresponding isomers for OH H2 On , except for the C3 , 3-1(2) and 4-1(2) isomers. In the C3 isomers, the larger (water-waterwater) 3-body term for OH H2 O3 is associated with smaller O-O separations between neighboring water molecules than for SH H2 O3 (fact (A)). Fully optimized structural parameters are available from the author (at no charge).
4. Conclusions (1) The relative stability of several isomers of SH H2 On is considerably dierent from that of corresponding isomers of OH H2 On (n 3±5): In OH H2 O3 ; C3 > 2 1 2; in SH H2 O3 ; C3 < 2 1 2. In OH H2 O4 ; C4 3 1 2 > 3 1 3 > 3 1 1; in SH H2 O4 ; C4 > 3 1 2 > 3 1 3 ; 3 1 1. In OH H2 O5 ; C5 4 1 1 < 4 1 2; in SH H2 O5 ; C5 > 4 1 1 ; 4 1 2. The OH ion starts with highly symmetric Cn structures with small degree of Hbonding between water molecules (n 3; 4) and progresses to asymmetric ones with water in the second solvation shell for n 5 whereas the trend is opposite for SH which starts with structures exhibiting stronger H-bonding between water molecules (2-1(1) isomer for n 3) and progresses to isomers with higher symmetry and less interwater H-bonding (Cn isomers for n 4; 5). The
n 4 cluster seems to be the turning point for both since for this cluster size the C4 and 3-1(2) isomers are close in energy. (2) We clarify the cause for the dierence by energy decomposition. Acknowledgements We are grateful to the Institute for Molecular Science for the use of computer time and the GA U S S I A N 94 and GA U S S I A N 98 programs. References [1] M. Arshadi, P. Kebarle, J. Phys. Chem. 74 (1970) 1483. [2] M.D. Newton, S. Ehrenson, J. Am. Chem. Soc. 93 (1971) 4971. [3] A.-M. Sapse, L. Osorio, G. Snyder, Int. J. Quantum Chem. 26 (1984) 223. [4] M. Meot-Ner (Mautner), J. Am. Chem. Soc. 108 (1986) 6189. [5] M. Meot-Ner (Mautner), C.V. Speller, J. Phys. Chem. 90 (1986) 6616. [6] J.D. Madura, W.L. Jorgensen, J. Am.Chem. Soc. 108 (1986) 2517. [7] G. Andaloro, M.A. Palazzo, M. Migliore, S.L. Fornnili, Chem. Phys. Lett. 201 (1988) 149. [8] M. Tuckerman, K. Lassonen, M. Sprik, M. Parrinello, J. Phys.: Condens. Matter 6 (1994) 93. [9] I. Tunon, D. Rinaldi, M.F. Ruiz-Lopez, J.L. Rivail, J. Phys. Chem. 99 (1995) 3798. [10] S.S. Xantheas, J. Am. Chem. Soc. 117 (1995) 10379. [11] A.R. Grimm, G.B. Bacskay, A.D. Haymet, Mol. Phys. 86 (1995) 369. [12] M. Tuckerman, K. Lassonen, M. Sprik, M. Parrinello, J. Chem. Phys. 103 (1995) 150. [13] M. Tuckerman, K. Lassonen, M. Sprik, M. Parrinello, J. Phys. Chem. 99 (1995) 5749. [14] M. Tuckerman, M. Sprik, M. Parrinello, Femtochemistry (1996) 578. [15] C.P. Del Valle, J.J. Novoa, Chem. Phys. Lett. 269 (1997) 401. [16] J.J. Novoa, F. Mota, C.P. Del Valle, M. Planas, J. Phys. Chem. A 101 (1997) 7842. [17] M. Masamura, J. Mol. Struct. (Theochem) 498 (2000) 87. [18] M. Masamura, J. Comput. Chem. 22 (2001) 31. [19] J. Gao, D.S. Garner, W.L. Jorgensen, J. Am. Chem. Soc. 108 (1986) 4784. [20] J.E. Del Bene, J. Phys. Chem. 92 (1988) 2874. [21] S.S. Xantheas, J. Chem. Phys. 100 (1994) 7523.
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