- Email: [email protected]
Structure, vibrational spectra and energetics of OBrO+
22 May 1998
Chemical Physics Letters 288 Ž1998. 307–310
Structure, vibrational spectra and energetics of OBrOq Joseph S. Francisco Department of Chemistry and Department of Earth and Atmospheric Sciences, Purdue UniÕersity, West Lafayette, IN 47907-1393, USA Received 26 January 1998; in final form 23 February 1998
Abstract Structural, energetic and vibrational frequency data for OBrOq are calculated at the MP2, MP4 and CCSDŽT. levels of theory. The adiabatic ionization potential for OBrO is estimated to be 234.3 " 3 kcal moly1, and is calibrated using the adiabatic ionization potential for OClO. From the calibration, the probable uncertainty in the adiabatic potential for OBrO is estimated. q 1998 Elsevier Science B.V. All rights reserved.
1. Introduction Bromine oxide accounts for up to 40% of the total ozone depletion in the stratosphere w1x. However, many of the molecular properties of the BrO x species are not well characterized w2x. In the bromine-sensitized photodecomposition of O 3 , one of the key radical species involved is OBrO. However, recent studies w3–5x have detected the formation of OBrO radicals in the process. The detection of OBrO in these studies suggests the potential importance of this molecule in atmospheric reactions. Only recently, the molecular structure of OBrO has been derived from millimeter and submillimeter spectroscopic studies w6,7x. Moreover, UV absorption and vibrational frequencies for the ground and excited states have been reported for OBrO w8x. At present, there is no direct determination of the heat of formation for OBrO. Chase w2x has provided an estimate of the heat of formation as 163 " 25 kJ moly1 . However, there is a large uncertainty with this value. The photoionization mass spectroscopic method has been demonstrated to be a reliable technique in determining the heats of formation for simple molecules. However, before such a technique can be used for
studies determining the energetic properties of OBrO, knowledge of the adiabatic ionization potential would be useful. In this work, post-Hartree–Fock ab initio methods are employed to calculate the adiabatic ionization potential energies for OBrO.
2. Methodology Equilibrium structures of the neutral and cation species of BrO and OBrO were obtained with four different electron correlation approaches. The simplest is the second-order Møller–Plesset perturbation theory ŽMP2. w9x with all electrons correlated. Fourth-order Møller–Plesset with single, double, triple and quadruple excitations included ŽMP4. w9x was also used. Single and double excitation coupled-cluster theory including a perturbational estimate of the effects of connected triple excitations ŽCCSDŽT.. w10,11x were the other two methods used. Only the valence electrons were included in the correlation procedure. Two basis sets were used. The first, denoted TZ2P, is comprised of Dunning’s w12x 5s3pr3s contractions for oxygen. The polarization
0009-2614r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 Ž 9 8 . 0 0 2 5 6 - 5
J.S. Franciscor Chemical Physics Letters 288 (1998) 307–310
308
orbital exponents Žtwo d-functions for oxygen. are taken from Dunning w13x. The Br TZ2P basis set is composed of a 6s5p2d contraction of a 17s13p6d primitive set given by Schaefer et al. w14x. The orbital exponents of the two d polarization functions are a d s 0.674 and 0.225. All six components of the Cartesian d-functions were included in the basis sets. Single-point energy calculations were performed with the split-valence triplet zeta basis augmented with three sets of d-functions, a set of diffuse functions, and a set of f-polarization functions of bromine and oxygen atoms. This comprised the 6-311q GŽ3df. basis set w15x. As a general strategy, the neutral and cation of BrO and OBrO were initially investigated at the unrestricted second-order Møller–Plesset ŽUMP2. level. All geometry optimizations were fully opti˚ for bond lengths and mized to better than 0.001 A 0.18 for angles. With a SCF convergence of at least 10y9 on the density matrix, the root-mean-square Žrms. force was 10y4 atomic units. After a complete geometry optimization, the nature of the stationary point on the potential energy surface was examined through calculations of the vibrational frequencies for that level of theory in the harmonic approximation. 3. Results and discussion The optimized geometries for OBrOq and its neutral species are given in Table 1. Submillimeter spectroscopic studies have confirmed that like OClO
w16x, the OBrO ground state possesses C 2v symmetry w5,6x. The calculations show that there is indeed an electron correlation effect on the structure. The MP2rTZ2P level predicts the BrO bond length to be ˚ for the experimental determination. within 0.003 A The MP4 level overestimates the BrO bond by 0.019 ˚ and at the same time overwidens the OBrO angle A, by 2.28. At the CCSDŽT. level of theory, the BrO ˚ of the experiment, and bond length is within 0.01 A ˚ is in excellent agreement with the angle of 114.8 A experiment. With the CCSDŽT.r6-31rGŽ2df. level of theory, the predicted BrO bond length is within ˚ for the experimental determination and the 0.005 A bond angle agrees well with experiment. These calculations suggest that both the MP2 and CCSDŽT. levels of theory provide reasonable estimates of the geometry for OBrO. It should be noted that the errors in the MP4 structural parameters for OBrO may point to basis set deficiencies in the TZ2P basis set. This is also seen by the significant basis set effect on the CCSDŽT. results. The good MP2rTZ2P result is partly due to error compensation. Moreover, an examination of the rotational constants for OBrO shows similar good agreement with experiment for both the MP2 and CCSDŽT. levels of theory. Removal of an electron from the neutral species to form the cation acts to strengthen the BrO bonds, as evidenced by a decrease in the BrO bond length in the cation relative to the neutral species. The MP4 level of theory shows an anomalous trend, with a ˚ increase in the BrO bond length. It should 0.011 A be noted that the MP4 level shows the largest angle
Table 1 Geometries and rotational constants for OBrO and OBrOq Species
OBrO
OBrOq
a
Levels of theory
MP2rTZ2P MP4rTZ2P CCSDŽT.rTZ2P CCSDŽT.r6-311GŽ2df. Expt.a MP2rTZ2P MP4rTZ2P CCSDŽT.rTZ2P CCSDŽT.r6-311GŽ2df.
Refs. w6x and w7x.
Geometric parameters
Rotational constants ŽMHz.
BrO ˚. ŽA
OBrO Ž8.
A
B
C
1.646 1.668 1.660 1.644 1.649 1.630 1.679 1.619 1.607
115.6 117.0 114.8 114.8 114.8 117.6 122.0 115.8 115.6
28870 29204 27784 28287 28024.51821 31131 33561 29963 30292
8134 7808 8070 8240 8233.172826 8154 7323 8401 8545
6346 6161 6254 6381 6345.433279 6449 6012 6561 6665
J.S. Franciscor Chemical Physics Letters 288 (1998) 307–310
309
Table 2 Harmonic vibrational frequencies Žin cmy1 . for OBrO and OBrOq Species
OBrO
OBrOq
a b
Mode number
1 2 3 1 2 3
Vibrational frequenciesa
Mode
Expt.b
Symmetry
Description
MP2
MP4
CCSDŽT.
a1
BrO sym. stretch OBrO bend BrO asym. stretch BrO sym. stretch OBrO bend BrO asym. stretch
880 320 918 854 323 992
822 292 846 788 270 1014
797 317 845 822 332 910
b2 a1 b2
799.4 317.5 848.6
Calculated with the TZ2P basis set. Ref. w8x.
change, compared to the other methods. Nevertheless, the MP2 and CCSDŽT. levels show a decrease ˚ respectively, in the BrO bond of 0.016 and 0.030 A, length for the cation. The angle in the cation shows a consistent trend of being wider than in its neutral form. At the CCSDŽT.rTZ2P level, the angle change is by 18. The harmonic vibrational frequencies for are given in Table 2 along with those for neutral OBrOq, for comparison. Examining the harmonic frequencies, the first point to note is that at all levels of electron correlation, the structures correspond to a minimum. Also, to be noted is that although the MP2 level gives a better structure than the CCSDŽT. level, the harmonic vibrational frequencies calculated with the CCSDŽT. method are in better agreement with the experiment. A comparison of vibrational modes of the neutral species to the equivalent modes OBrOq of reveals that there are significant shifts. The BrO symmetric stretching mode Ž n 1 . shifts by 25 cmy1 to the blue, and the BrO asymmetric stretching mode Ž n 3 . shifts by 65y1 to the blue. These shifts suggest that the BrO bonds are stronger in OBrOq than in its
neutral form. This is consistent with the change in bond lengths predicted for OBrOq. The total ŽTable 3. and zero-point energies Žcalculated from vibrational frequencies in Table 2. of OBrOq are combined with corresponding energies of the neutral OBrO to compute the adiabatic ionization energy for OBrO. From Table 3, the adiabatic ionization energy for OBrO is estimated to range between 209.3 and 234.4 kcal moly1 for the MP2, MP4 and CCSDŽT. levels of theory. The variations in the values suggest electron correlation dependences in the adiabatic ionization energy. At the CCSDŽT.rTZ2P level, the adiabatic ionization energy is estimated to be 228.3 kcal moly1 . To refine this value, a single-point energy calculation was performed with the larger 6-311 q GŽ3df. basis set using the CCSDŽT.rTZ2P geometry Žhence a CCSDŽT.r6-311 q GŽ3df.rrCCSDŽT.rTZ2P calculation.. The adiabatic ionization energy is estimated as 234.4 kcal moly1 . The CCSDŽT.r6-311q GŽ3df.rrCCSDŽT.r6-311GŽ2df. energy value is 234.3 kcal moly1 . There is no report in the literature of the adiabatic
Table 3 Total and relative energies for OBrO and OBrOq Levels of theory
MP2rTZ2P MP4rTZ2P CCSDŽT.rTZ2P CCSDŽT.r6-311GŽ2df. CCSDŽT.r6-311q GŽ3df.rrCCSDŽT.rTZ2P CCSDŽT.r6-311q GŽ3df.rrCCSDŽT.r6-311GŽ2df.
Total energies Žhartree.
Adiabatic IP
OBrO
OBrOq
y2722.42465 y2722.69479 y2722.67853 y2722.59017 y2722.62445 y2722.62470
y2722.42465 y2722.36116 y2722.31466 y2722.22520 y2722.25091 y2722.25142
217.0 209.3 228.3 229.1 234.4 234.3
J.S. Franciscor Chemical Physics Letters 288 (1998) 307–310
310
Table 4 Calibration of adiabatic ionization energy using OClO Species
OCl
OClOq
Methods
OCCSDŽT.r6-311GŽ2df. CCSD.T.r6-311q GŽ3df.rrCCSDŽT.r6-311GŽ2df. CMRCIq Q d CCSDŽT.r6-311GŽ2df. CCSDŽT.r6-311q GŽ3df.rrCCSDŽT.r6-311GŽ2df. CMRCIq Q d Expt.e
Geometriesa
Total and relative energies
ClO
OClO
Energy b
1.487
117.6
y609.75190 y609.78784
1.488 1.429
117.4 120.0
1.431
120.6
y609.38397 y609.41173
IP c
230.9Ž10.0. 236.1Ž10.3. 232.1Ž10.08. 237.9 " 0.5Ž10.33 " 0.02.
a
˚ and bond angle in degrees. Bond distances are in units of A Energy in units of hartree. c In units of kcal moly1 ; numbers in parentheses are in units of eV. d Ref. w17x. e Ref. w18x. b
ionization potential for OBrO. To examine the reliability of the result predicted at the CCSDŽT.r6-311 q GŽ3df.rrCCSDŽT.r6-311GŽ2df. level of theory for OBrO, the adiabatic ionization energy for OClO is estimated. Petersen and Werner w17x estimated the adiabatic ionization of OClO using CMRCIq Q and obtained a value of 232.1 kcal moly1 Ž10.08 eV.. At the CCSD ŽT .r6-311 q G Ž3df.rrCCSD ŽT .r6311GŽ2df. level of theory, Žsee Table 4., the adiabatic ionization energy for OClO is predicted to be 236.1 kcal moly1 . This compares to 237.9 " 0.5 kcal moly1 determined by the experiments of Flesch et al. w18x, for which there is a ca. 2 kcal moly1 difference between experimental and theoretical results. A more conservative estimate for the uncertainty in the ab initio estimate for OBrO is "3 kcal moly1 . Given this uncertainty, the adiabatic ionization energy for OBrO should be reasonably determined.
References w1x R.P. Wayne, G. Poulet, P. Biggs, J.P. Burrows, R.A. Cox, P.J. Crutzen, G.D. Hayman, M.E. Jenkins, G. LeBras, G.K. Moortgat, U. Platt, R.N. Schindler, Atmos. Environ. 29 Ž1995. 2677.
w2x M.W. Chase, J. Phys. Chem. Ref. Data 25 Ž1996. 1069. w3x O.V. Rattigan, R.L. Jones, R.A. Cox, Chem. Phys. Lett. 230 Ž1994. 121. w4x O.V. Rettigan, R.L. Jones, R.A. Cox, J. Chem. Soc., Faraday Trans. 91 Ž1995. 4189. w5x D.M. Rowley, M.H. Harwood, R.A. Freshwater, R.L. Jones, J. Phys. Chem. 100 Ž1996. 3020. w6x H.S.P. Muller, C.E. Miller, E.A. Cohen, Angew. Chem. 108 Ž1996. 2285. w7x H.S.P. Muller, C.E. Miller, E.A. Cohen, Angew. Chem. Int. Ed. Engl. 35 Ž1996. 2129. w8x C.E. Miller, S.L. Nickolaisen, J.S. Francisco, S.P. Sander, J. Chem. Phys. 107 Ž1997. 2300. w9x J.A. Pople, R. Krishnan, H.B. Schlegel, J.S. Binkley, Int. J. Quant. Chem. 13 Ž1979. 225. w10x G.D. Purvis III, R. Bartlett, J. Chem. Phys. 76 Ž1982. 1910. w11x T.J. Lee, A.P. Rendell, J. Chem. Phys. 94 Ž1991. 6229. w12x T.H. Dunning, J. Chem. Phys. 55 Ž1971. 716. w13x T.H. Dunning, J. Chem. Phys. 90 Ž1989. 1007. w14x A. Schaefer, C. Huber, R. Ahlrichs, J. Chem. Phys. 100 Ž1994. 5829. w15x L.A. Curtiss, M.P. McGrath, J.P. Blaudeau, N.E. Davis, R.C. Binning Jr., L. Radom, J. Chem. Phys. 103 Ž1995. 6104. w16x R.F. Carl, R.F. Heidelberg, J.L. Kinsey, Phys. Rev. 125 Ž1962. 1993. w17x K.A. Peterson, H.J. Werner, J. Chem. Phys. 99 Ž1993. 302. w18x R. Flesch, E. Ruhl, K. Hoffmann, H. Baumgartel, J. Phys. Chem. 97 Ž1993. 837.
Chemical Physics Letters 288 Ž1998. 307–310
Structure, vibrational spectra and energetics of OBrOq Joseph S. Francisco Department of Chemistry and Department of Earth and Atmospheric Sciences, Purdue UniÕersity, West Lafayette, IN 47907-1393, USA Received 26 January 1998; in final form 23 February 1998
Abstract Structural, energetic and vibrational frequency data for OBrOq are calculated at the MP2, MP4 and CCSDŽT. levels of theory. The adiabatic ionization potential for OBrO is estimated to be 234.3 " 3 kcal moly1, and is calibrated using the adiabatic ionization potential for OClO. From the calibration, the probable uncertainty in the adiabatic potential for OBrO is estimated. q 1998 Elsevier Science B.V. All rights reserved.
1. Introduction Bromine oxide accounts for up to 40% of the total ozone depletion in the stratosphere w1x. However, many of the molecular properties of the BrO x species are not well characterized w2x. In the bromine-sensitized photodecomposition of O 3 , one of the key radical species involved is OBrO. However, recent studies w3–5x have detected the formation of OBrO radicals in the process. The detection of OBrO in these studies suggests the potential importance of this molecule in atmospheric reactions. Only recently, the molecular structure of OBrO has been derived from millimeter and submillimeter spectroscopic studies w6,7x. Moreover, UV absorption and vibrational frequencies for the ground and excited states have been reported for OBrO w8x. At present, there is no direct determination of the heat of formation for OBrO. Chase w2x has provided an estimate of the heat of formation as 163 " 25 kJ moly1 . However, there is a large uncertainty with this value. The photoionization mass spectroscopic method has been demonstrated to be a reliable technique in determining the heats of formation for simple molecules. However, before such a technique can be used for
studies determining the energetic properties of OBrO, knowledge of the adiabatic ionization potential would be useful. In this work, post-Hartree–Fock ab initio methods are employed to calculate the adiabatic ionization potential energies for OBrO.
2. Methodology Equilibrium structures of the neutral and cation species of BrO and OBrO were obtained with four different electron correlation approaches. The simplest is the second-order Møller–Plesset perturbation theory ŽMP2. w9x with all electrons correlated. Fourth-order Møller–Plesset with single, double, triple and quadruple excitations included ŽMP4. w9x was also used. Single and double excitation coupled-cluster theory including a perturbational estimate of the effects of connected triple excitations ŽCCSDŽT.. w10,11x were the other two methods used. Only the valence electrons were included in the correlation procedure. Two basis sets were used. The first, denoted TZ2P, is comprised of Dunning’s w12x 5s3pr3s contractions for oxygen. The polarization
0009-2614r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 Ž 9 8 . 0 0 2 5 6 - 5
J.S. Franciscor Chemical Physics Letters 288 (1998) 307–310
308
orbital exponents Žtwo d-functions for oxygen. are taken from Dunning w13x. The Br TZ2P basis set is composed of a 6s5p2d contraction of a 17s13p6d primitive set given by Schaefer et al. w14x. The orbital exponents of the two d polarization functions are a d s 0.674 and 0.225. All six components of the Cartesian d-functions were included in the basis sets. Single-point energy calculations were performed with the split-valence triplet zeta basis augmented with three sets of d-functions, a set of diffuse functions, and a set of f-polarization functions of bromine and oxygen atoms. This comprised the 6-311q GŽ3df. basis set w15x. As a general strategy, the neutral and cation of BrO and OBrO were initially investigated at the unrestricted second-order Møller–Plesset ŽUMP2. level. All geometry optimizations were fully opti˚ for bond lengths and mized to better than 0.001 A 0.18 for angles. With a SCF convergence of at least 10y9 on the density matrix, the root-mean-square Žrms. force was 10y4 atomic units. After a complete geometry optimization, the nature of the stationary point on the potential energy surface was examined through calculations of the vibrational frequencies for that level of theory in the harmonic approximation. 3. Results and discussion The optimized geometries for OBrOq and its neutral species are given in Table 1. Submillimeter spectroscopic studies have confirmed that like OClO
w16x, the OBrO ground state possesses C 2v symmetry w5,6x. The calculations show that there is indeed an electron correlation effect on the structure. The MP2rTZ2P level predicts the BrO bond length to be ˚ for the experimental determination. within 0.003 A The MP4 level overestimates the BrO bond by 0.019 ˚ and at the same time overwidens the OBrO angle A, by 2.28. At the CCSDŽT. level of theory, the BrO ˚ of the experiment, and bond length is within 0.01 A ˚ is in excellent agreement with the angle of 114.8 A experiment. With the CCSDŽT.r6-31rGŽ2df. level of theory, the predicted BrO bond length is within ˚ for the experimental determination and the 0.005 A bond angle agrees well with experiment. These calculations suggest that both the MP2 and CCSDŽT. levels of theory provide reasonable estimates of the geometry for OBrO. It should be noted that the errors in the MP4 structural parameters for OBrO may point to basis set deficiencies in the TZ2P basis set. This is also seen by the significant basis set effect on the CCSDŽT. results. The good MP2rTZ2P result is partly due to error compensation. Moreover, an examination of the rotational constants for OBrO shows similar good agreement with experiment for both the MP2 and CCSDŽT. levels of theory. Removal of an electron from the neutral species to form the cation acts to strengthen the BrO bonds, as evidenced by a decrease in the BrO bond length in the cation relative to the neutral species. The MP4 level of theory shows an anomalous trend, with a ˚ increase in the BrO bond length. It should 0.011 A be noted that the MP4 level shows the largest angle
Table 1 Geometries and rotational constants for OBrO and OBrOq Species
OBrO
OBrOq
a
Levels of theory
MP2rTZ2P MP4rTZ2P CCSDŽT.rTZ2P CCSDŽT.r6-311GŽ2df. Expt.a MP2rTZ2P MP4rTZ2P CCSDŽT.rTZ2P CCSDŽT.r6-311GŽ2df.
Refs. w6x and w7x.
Geometric parameters
Rotational constants ŽMHz.
BrO ˚. ŽA
OBrO Ž8.
A
B
C
1.646 1.668 1.660 1.644 1.649 1.630 1.679 1.619 1.607
115.6 117.0 114.8 114.8 114.8 117.6 122.0 115.8 115.6
28870 29204 27784 28287 28024.51821 31131 33561 29963 30292
8134 7808 8070 8240 8233.172826 8154 7323 8401 8545
6346 6161 6254 6381 6345.433279 6449 6012 6561 6665
J.S. Franciscor Chemical Physics Letters 288 (1998) 307–310
309
Table 2 Harmonic vibrational frequencies Žin cmy1 . for OBrO and OBrOq Species
OBrO
OBrOq
a b
Mode number
1 2 3 1 2 3
Vibrational frequenciesa
Mode
Expt.b
Symmetry
Description
MP2
MP4
CCSDŽT.
a1
BrO sym. stretch OBrO bend BrO asym. stretch BrO sym. stretch OBrO bend BrO asym. stretch
880 320 918 854 323 992
822 292 846 788 270 1014
797 317 845 822 332 910
b2 a1 b2
799.4 317.5 848.6
Calculated with the TZ2P basis set. Ref. w8x.
change, compared to the other methods. Nevertheless, the MP2 and CCSDŽT. levels show a decrease ˚ respectively, in the BrO bond of 0.016 and 0.030 A, length for the cation. The angle in the cation shows a consistent trend of being wider than in its neutral form. At the CCSDŽT.rTZ2P level, the angle change is by 18. The harmonic vibrational frequencies for are given in Table 2 along with those for neutral OBrOq, for comparison. Examining the harmonic frequencies, the first point to note is that at all levels of electron correlation, the structures correspond to a minimum. Also, to be noted is that although the MP2 level gives a better structure than the CCSDŽT. level, the harmonic vibrational frequencies calculated with the CCSDŽT. method are in better agreement with the experiment. A comparison of vibrational modes of the neutral species to the equivalent modes OBrOq of reveals that there are significant shifts. The BrO symmetric stretching mode Ž n 1 . shifts by 25 cmy1 to the blue, and the BrO asymmetric stretching mode Ž n 3 . shifts by 65y1 to the blue. These shifts suggest that the BrO bonds are stronger in OBrOq than in its
neutral form. This is consistent with the change in bond lengths predicted for OBrOq. The total ŽTable 3. and zero-point energies Žcalculated from vibrational frequencies in Table 2. of OBrOq are combined with corresponding energies of the neutral OBrO to compute the adiabatic ionization energy for OBrO. From Table 3, the adiabatic ionization energy for OBrO is estimated to range between 209.3 and 234.4 kcal moly1 for the MP2, MP4 and CCSDŽT. levels of theory. The variations in the values suggest electron correlation dependences in the adiabatic ionization energy. At the CCSDŽT.rTZ2P level, the adiabatic ionization energy is estimated to be 228.3 kcal moly1 . To refine this value, a single-point energy calculation was performed with the larger 6-311 q GŽ3df. basis set using the CCSDŽT.rTZ2P geometry Žhence a CCSDŽT.r6-311 q GŽ3df.rrCCSDŽT.rTZ2P calculation.. The adiabatic ionization energy is estimated as 234.4 kcal moly1 . The CCSDŽT.r6-311q GŽ3df.rrCCSDŽT.r6-311GŽ2df. energy value is 234.3 kcal moly1 . There is no report in the literature of the adiabatic
Table 3 Total and relative energies for OBrO and OBrOq Levels of theory
MP2rTZ2P MP4rTZ2P CCSDŽT.rTZ2P CCSDŽT.r6-311GŽ2df. CCSDŽT.r6-311q GŽ3df.rrCCSDŽT.rTZ2P CCSDŽT.r6-311q GŽ3df.rrCCSDŽT.r6-311GŽ2df.
Total energies Žhartree.
Adiabatic IP
OBrO
OBrOq
y2722.42465 y2722.69479 y2722.67853 y2722.59017 y2722.62445 y2722.62470
y2722.42465 y2722.36116 y2722.31466 y2722.22520 y2722.25091 y2722.25142
217.0 209.3 228.3 229.1 234.4 234.3
J.S. Franciscor Chemical Physics Letters 288 (1998) 307–310
310
Table 4 Calibration of adiabatic ionization energy using OClO Species
OCl
OClOq
Methods
OCCSDŽT.r6-311GŽ2df. CCSD.T.r6-311q GŽ3df.rrCCSDŽT.r6-311GŽ2df. CMRCIq Q d CCSDŽT.r6-311GŽ2df. CCSDŽT.r6-311q GŽ3df.rrCCSDŽT.r6-311GŽ2df. CMRCIq Q d Expt.e
Geometriesa
Total and relative energies
ClO
OClO
Energy b
1.487
117.6
y609.75190 y609.78784
1.488 1.429
117.4 120.0
1.431
120.6
y609.38397 y609.41173
IP c
230.9Ž10.0. 236.1Ž10.3. 232.1Ž10.08. 237.9 " 0.5Ž10.33 " 0.02.
a
˚ and bond angle in degrees. Bond distances are in units of A Energy in units of hartree. c In units of kcal moly1 ; numbers in parentheses are in units of eV. d Ref. w17x. e Ref. w18x. b
ionization potential for OBrO. To examine the reliability of the result predicted at the CCSDŽT.r6-311 q GŽ3df.rrCCSDŽT.r6-311GŽ2df. level of theory for OBrO, the adiabatic ionization energy for OClO is estimated. Petersen and Werner w17x estimated the adiabatic ionization of OClO using CMRCIq Q and obtained a value of 232.1 kcal moly1 Ž10.08 eV.. At the CCSD ŽT .r6-311 q G Ž3df.rrCCSD ŽT .r6311GŽ2df. level of theory, Žsee Table 4., the adiabatic ionization energy for OClO is predicted to be 236.1 kcal moly1 . This compares to 237.9 " 0.5 kcal moly1 determined by the experiments of Flesch et al. w18x, for which there is a ca. 2 kcal moly1 difference between experimental and theoretical results. A more conservative estimate for the uncertainty in the ab initio estimate for OBrO is "3 kcal moly1 . Given this uncertainty, the adiabatic ionization energy for OBrO should be reasonably determined.
References w1x R.P. Wayne, G. Poulet, P. Biggs, J.P. Burrows, R.A. Cox, P.J. Crutzen, G.D. Hayman, M.E. Jenkins, G. LeBras, G.K. Moortgat, U. Platt, R.N. Schindler, Atmos. Environ. 29 Ž1995. 2677.
w2x M.W. Chase, J. Phys. Chem. Ref. Data 25 Ž1996. 1069. w3x O.V. Rattigan, R.L. Jones, R.A. Cox, Chem. Phys. Lett. 230 Ž1994. 121. w4x O.V. Rettigan, R.L. Jones, R.A. Cox, J. Chem. Soc., Faraday Trans. 91 Ž1995. 4189. w5x D.M. Rowley, M.H. Harwood, R.A. Freshwater, R.L. Jones, J. Phys. Chem. 100 Ž1996. 3020. w6x H.S.P. Muller, C.E. Miller, E.A. Cohen, Angew. Chem. 108 Ž1996. 2285. w7x H.S.P. Muller, C.E. Miller, E.A. Cohen, Angew. Chem. Int. Ed. Engl. 35 Ž1996. 2129. w8x C.E. Miller, S.L. Nickolaisen, J.S. Francisco, S.P. Sander, J. Chem. Phys. 107 Ž1997. 2300. w9x J.A. Pople, R. Krishnan, H.B. Schlegel, J.S. Binkley, Int. J. Quant. Chem. 13 Ž1979. 225. w10x G.D. Purvis III, R. Bartlett, J. Chem. Phys. 76 Ž1982. 1910. w11x T.J. Lee, A.P. Rendell, J. Chem. Phys. 94 Ž1991. 6229. w12x T.H. Dunning, J. Chem. Phys. 55 Ž1971. 716. w13x T.H. Dunning, J. Chem. Phys. 90 Ž1989. 1007. w14x A. Schaefer, C. Huber, R. Ahlrichs, J. Chem. Phys. 100 Ž1994. 5829. w15x L.A. Curtiss, M.P. McGrath, J.P. Blaudeau, N.E. Davis, R.C. Binning Jr., L. Radom, J. Chem. Phys. 103 Ž1995. 6104. w16x R.F. Carl, R.F. Heidelberg, J.L. Kinsey, Phys. Rev. 125 Ž1962. 1993. w17x K.A. Peterson, H.J. Werner, J. Chem. Phys. 99 Ž1993. 302. w18x R. Flesch, E. Ruhl, K. Hoffmann, H. Baumgartel, J. Phys. Chem. 97 Ž1993. 837.