Conformational landscape of the weakly bound difluoromethane–1,1-difluoroethane dimer explored by rotational spectroscopy and quantum chemical calculations

Journal of Molecular Spectroscopy 357 (2019) 32–37

Contents lists available at ScienceDirect

Journal of Molecular Spectroscopy journal homepage: www.elsevier.com/locate/jms

Conformational landscape of the weakly bound difluoromethane–1, 1-difluoroethane dimer explored by rotational spectroscopy and quantum chemical calculations Tao Lu a, Junhua Chen a, Jiaqi Zhang a, Qian Gou a,b, Zhining Xia a, Gang Feng a,b,⇑ a b

School of Chemistry and Chemical Engineering, Chongqing University, Daxuecheng South Rd. 55, 401331 Chongqing, China Collaborative Innovation Center for Brain Science, Chongqing University, No. 174 Shazhengjie, Shapingba, 400044 Chongqing, China

a r t i c l e

i n f o

Article history: Received 4 December 2018 In revised form 14 January 2019 Accepted 10 February 2019 Available online 12 February 2019 Keywords: Conformational equilibria Microwave spectroscopy Weak hydrogen bond Supersonic expansion

a b s t r a c t The rotational spectra of three isomers of the difluoromethane–1,1-difluoroethane dimer were measured and assigned by using Fourier transform microwave spectroscopy. Experimental results, ab initio calculations and quantum theory of atoms in molecules (QTAIM) analysis confirm that the two subunits in the observed isomers are held together by three weak CAH


FAC interactions. Rotational spectra of all the 13C isotopologues were also observed for all the three isomers. The experimental data leads to precise determination of the substitution (rs) and effective (r0) structures of the observed isomers. The Symmetry-adapted perturbation theory (SAPT) analysis demonstrates that electrostatic and dispersion terms play a major role in determining the stabilities of the complex. The relative populations of the three observed isomers in the supersonic expansion in helium were estimated as NI/NII/NIII  5/2/6 from relative intensity measurements. Ó 2019 Elsevier Inc. All rights reserved.

1. Introduction Considerable effort has been devoted to the investigation of weak hydrogen bonds (WHBs) such as CAH


O and CAH


XAC (X = F and Cl) due to their important roles in biological, supramolecular and atmospheric chemistry [1–3]. Studies on such WHBs have mainly implemented by means of X-ray diffraction [4], IR spectroscopy in rare-gas solutions [5,6] and rotational spectroscopy combined with supersonic expansions [7,8]. Solid-state or solution-phase investigations are contaminated from the crystal or solvent effect whereas gas-phase investigations can directly provide detailed information on the specific of local WHBs [9]. Molecular clusters of halocarbon in gas-phase appear to be the prototypes for investigating the nature of WHBs. Halocarbon containing hydrogen atoms can simultaneously act as weak proton donors and acceptors, forming clusters with formaldehyde [10,11] or water [12–15] through H


XAC interaction in cooperation with CAH


O WHBs. In halocarbon containing both fluorine and chlorine atoms, OAH


ClAC interaction is preferred in the clusters of water with CH2ClF [14] and CHClF2 [15], whereas OAH


FAC interaction is the main contributor for forming the ⇑ Corresponding author at: School of Chemistry and Chemical Engineering, Chongqing University, Daxuecheng South Rd. 55, 401331 Chongqing, China. E-mail address: [email protected] (G. Feng). https://doi.org/10.1016/j.jms.2019.02.002 0022-2852/Ó 2019 Elsevier Inc. All rights reserved.

CH3CHFCl


H2O cluster [12]. Per-halogenated halocarbon forms halogen bonds with partner molecules [16–21]. Furthermore, a lone pair


p linkage has been favoured [22–24] when there is a p orbital in the per-halogenated halocarbon. Halocarbon containing hydrogen atoms also tends to form weakly bound homo- or hetero-clusters. Difluoromethane (CH2F2, DFM) is a simple asymmetric molecule containing two proton donors and two proton acceptors. The dimer [25], trimer [26], and tetramer [27] of DFM are held together via a network of 3, 9, and 16 CAH


FAC WHBs, respectively, as revealed by microwave spectroscopy. Recently, the 1,1-difluoroethane (CH3CHF2, DFE) [28] dimer and 1,1,1,2-tetrafluoroethane (CF3CH2F, TFE) [29] dimer have been investigated, which are stabilized by three and four CAH


FAC WHBs, respectively. The CAH


FAC interaction dominates the stabilization of the hetero-dimers of DFM with several fluorinated ethylenes [30,31] and TFE [32] as well as CHF3


CH3F [33]. For chlorine contained molecules, CAH


ClAC interaction in combination with one or two CAH


FAC linkages lead to the stabilization of the clusters [34–36]. Usually, only one conformation in the supersonic expansion could be detected for these clusters. Exceptions have been reported for the DFE dimer in which two most stable isomers predicted by ab initio have been detected [28] and for the DFM-TFE heterodimer in which three isomers have been detected [32]. The presence of multiple conformations is likely due to the increase of the alkyl

33

T. Lu et al. / Journal of Molecular Spectroscopy 357 (2019) 32–37

chain which provides additional sites of complexation. However, investigations on conformational complexity in term of monomer structure are limited. In this context, with the aim to gain insight into the multiple configurations of CAH


FAC bound clusters, the DFM-DFE dimer was studied by using pulsed-jet Fourier transform microwave (FTMW) spectroscopy coupled with quantum chemical calculations.

Table 1 Relative energies, zero point dissociation energies, rotational constants, planar moments of inertia and dipole moment components of the three most stable isomers of DFM-DFE calculated at the MP2/6-311++G(d, p) level of theory.

2. Experimental The rotational spectra of the DFM-DFE cluster have been recorded in the frequency range 2–20 GHz by utilizing a COBRA (Coaxially Aligned Beam Resonator Arrangement) [37] pulsed supersonic-jet FTMW spectrometer [38] at Chongqing University [39]. The spectrometer is operated by using the FTMW++ set of programs [40]. The estimated accuracy of the frequency measurements is better than 3 kHz. The instrumental resolution is better than 6 kHz. All samples were obtained commercially and used without further purification. A sample of gas mixture of approximately 1% DFM and 1% DFE in Helium (or Ar) was prepared in a stainless steel tank. The resultant mixture was stagnated at a constant pressure of 0.3 MPa and expanded through the solenoid valve (General Valve, Series 9, nozzle diameter 0.5 mm) into the Fabry-Pérot-type cavity. The spectral line positions were determined after Fourier transform of the time-domain signal with 8 k data points, recorded with 100 ns sample intervals. Each rotational transition appears as a doublet due to the Doppler effect originating from the COBRA arrangement. The line position is calculated as the arithmetic mean of the frequencies of the Doppler components.

3. Results and discussion 3.1. Theoretical calculations Full geometry optimizations of the possible configurations of the DFM-DFE dimer were carried out at the MP2/6-311++G(d,p) level of theory. The obtained structures were confirmed to be the real minima by harmonic vibrational frequency analysis, which also provides the zero-point energies (ZPE). The basis set superposition error (BSSE) was counterpoise corrected [41]. All the calculations were performed by using the Gaussian16 program packages [42]. Multiple configurations for the DFM-DFE dimer arise when one of the hydrogen atoms in DFM is replaced by a ACH3 group. Three most stable isomers within 80 cm1 were found, whose shapes are displayed in Fig. 1. The relative energies, rotational constants, electric dipole moment components and planar moments of inertia of the three isomers are collected in Table 1, in which the calculated zero-point dissociation energies including BSSE corrections (ED) are also provided. The differences of the relative energies and dissociation energies of the three isomers are rather small practically within the accuracy of level of theory. All the isomers are stabilized through 3 CAH


FAC WHBs with distances ranging from 2.52 to 2.69 Å.

a b c d

Parameter

I

II

III

DE (cm1)a DE0 (cm1)b DE0,BSSE (cm1)c ED (kJ mol1) A (MHz) B (MHz) C (MHz) Paa (uÅ2)d Pbb (uÅ2) Pcc (uÅ2) |la| (D) |lb| (D) |lc| (D)

0 22 69 6.4 4246 1114 1026 413.59 79.07 39.94 2.0 0.3 0.2

31 0 0 7.2 4313 1027 990 442.66 67.95 49.22 3.3 0.2 0.0

32 25 50 6.6 6027 924 898 512.91 49.78 34.06 3.0 0.0 0.1

Relative value of the sum of electronic energy. Relative energy with zero-point energy correction. Relative energy with zero-point energy and BSSE correction. Planar moments of inertia, Pgg = Rimig2i , g = a, b and c.

3.2. Rotational spectra Following the ab initio predictions, spectral search was first targeted to the a- type R-brand of all the three isomers. After the transition lines belonging to the DFE monomer [43], DFE dimer [28], and DFM trimer [26] were removed from the spectrum, several groups of lines belonging to (J + 1) J band, Ka = 0,1 transitions for isomer II were observed and assigned first. Then, the measurements of a-type transitions were extended to the J = 3–10 with Ka up to 5, from which the three rotational constants (A, B and C) can be well determined. No lines belonging to b- and c-type transitions for this isomer could be observed, in agreement with the very small values of the lb and lc dipole moment components. After transition lines of isomer II were excluded from the spectrum, plenty of relatively intense transitions could be assigned to isomer III. A total of 63 a-R type transitions with J = 2–10 and Ka = 0–5 were measured. With further signal accumulation, 12 ctype transitions were also measured. None of b-type transition was observed, in accord with the zero value of lb dipole moment component. Finally, the spectrum of isomer I was searched, succeeding in measuring 62 a-type transitions with J = 2–8 and Ka = 0–5. Then, 8 b-type and 15 c-type transitions were measured by further signal accumulation. A section of spectrum showing the assignment of the three observed isomers is displayed in Fig. 2. All the measured transition lines were fitted, independently for each isomer, by utilizing Pickett’s SPFIT program [44] with Watson’s semirigid Hamiltonian (S-reduction in the Ir representation [45]), according to the following Hamiltonian:

H ¼ HR þ HCD ;

ð1Þ

where HR denotes the rigid rotational part of the Hamiltonian and HCD takes into account the corresponding centrifugal distortion contributions.

Fig. 1. Shapes, atomic numbering and the principal axes of inertia of the three isomers of the DFM-DFE dimer.

34

T. Lu et al. / Journal of Molecular Spectroscopy 357 (2019) 32–37

procedure as those of parent ones. Only two centrifugal distortion constants (DJ and DJK) can be determined, due to much fewer lines could be measured. Therefore, the values of other centrifugal distortion constants were fixed at the corresponding values of the parent species. The resulting spectroscopic parameters for the four isotopologues of isomers I, II and III are reported in Tables 2–4, respectively, where the experimental planar moments of inertia are also included. The measured rotational frequencies for all the isotopologues are given in the Supplementary Material. 3.3. Conformational information

Fig. 2. A section of spectrum recorded with 512 averages using a gas mixture of DFM (1%) and DFE (1%) in Helium. The upper trace is the experimentally obtained spectra while the lower trace is the stick spectra showing the assignments (given in red, green and blue for isomer I, II and III respectively) of the three isomers of the DFM-DFE dimer. M labels transition of the DFE monomer. Ns indicate transition lines of the DFE homodimer. Xs denote the transition lines of the DFM homotrimer.

Besides the most abundant species, the rotational spectra of the three 13C isotopologues for each isomer were also measured in natural abundance. The measured lines were analyzed with the same Table 2 Experimental spectroscopic parameters of the parent and the

A (MHz) B (MHz) C (MHz) DJ (kHz) DJK (kHz) DK (kHz) d1 (Hz) d2 (Hz) HJK (Hz) HKJ (Hz) Paa (uÅ2) Pbb (uÅ2) Pcc (uÅ2) rc (kHz) Nd a b c d

13

C1

C2

C9

4377.642(2)a 1053.6721(2) 990.3881(2) 1.781(2) 16.63(3) 25.8(5) 332(1) 70.2(9) 3.2(2) 29.3(9) 437.24 73.05 42.40 1.8 85

4299.7(4) 1049.4906(5) 983.4748(5) 1.726(4) 17.1(1) [25.8]b [332] [70.2] [3.2] [29.3] 438.94 74.93 42.61 3.2 21

4375.7(5) 1049.0267(6) 986.3795(6) 1.772(7) 16.5(1) [25.8] [332] [70.2] [3.2] [29.3] 439.31 73.05 42.45 1.6 18

4367.3(8) 1042.6906(6) 980.5011(6) 1.711(9) 16.8(1) [25.8] [332] [70.2] [3.2] [29.3] 442.20 73.23 42.49 2.2 15

Errors in parentheses are expressed in units of the last digit. Centrifugal distortion constants were fixed at the values of the parent species. Standard deviation of the fit. Number of transitions in the fit.

A (MHz) B (MHz) C (MHz) DJ (kHz) DJK (kHz) d2 (Hz) Paa (uÅ2) Pbb (uÅ2) Pcc (uÅ2) rc (kHz) Nd a

c d

C isotopologues of isomer I.

Parent

Table 3 Experimental spectroscopic parameters of the parent and three

b

For isomers II and III, the conformational assignment is straightforward by comparing the experimental rotational constants and the planar moments of inertia (Tables 3 and 4) to those of theoretical ones (Table 1). However, the theoretical rotational constant A of isomer I is smaller than the experimental one about 3.0% whereas the theoretical A constant of isomers II and III is larger than those of experimental ones about 1.7% and 1.0% (Tables 1 and 2). Firstly, we assumed other possible configurations were missed by the calculations. In this case, theoretical searching for other possible configurations were performed at the MP2/6-311++G(d,p) level of theory but all the starting geometries relaxed to those isomers shown in Fig. 1. Later on, geometry optimizations to isomers I, II and III were further performed at several different levels of theory. The results are summarized in Table 5. For isomer I, the xB97XD/6311++G(d,p) level of theory predicts rotational constants A, B and C about 0.03%, 0.1% and 0.8% different from the experimental values,

13

C isotopologues of isomer II.

Parent

C1

C2

C9

4255.1(2)a 1009.0495(2) 968.7195(2) 0.8936(9) 14.284(8) 0.0157(8) 451.89 69.81 48.96 2.9 62

4200(1) 1000.2314(5) 957.7389(5) 0.861(7) 13.7(1) [0.0157]b 456.31 71.37 48.96 1.8 17

4254(1) 1000.9886(5) 961.1788(5) 0.879(7) 14.1(1) [0.0157] 455.94 69.86 48.95 1.0 17

4253(1) 1002.9844(5) 963.0349(5) 0.886(7) 14.2(1) [0.0157] 454.91 69.87 48.96 1.7 17

Errors in parentheses are expressed in units of the last digit. Centrifugal distortion constants were fixed at the values of the parent species. Standard deviation of the fit. Number of transitions in the fit.

35

T. Lu et al. / Journal of Molecular Spectroscopy 357 (2019) 32–37 Table 4 Experimental spectroscopic parameters of the parent and three

13

C isotopologues of isomer III.

Parent A (MHz) B (MHz) C (MHz) DJ (kHz) DJK (kHz) DK (kHz) d1 (Hz) d2 (Hz) Paa (uÅ2) Pbb (uÅ2) Pcc (uÅ2) rc (kHz) Nd a b c d

5971.755(4) 900.9670(2) 879.2149(2) 0.5531(7) 14.377(9) 28.6(9) 20.3(8) 5.1(5) 525.55 49.25 35.38 2.7 75

a

C1

C2

C9

5963(5) 885.4492(4) 864.5525(4) 0.523(3) 13.72(9) [28.6]b [20.3] [5.1] 535.28 49.27 35.48 1.4 22

5971(3) 896.6326(3) 875.1772(3) 0.550(2) 14.2(4) [28.6] [20.3] [5.1] 528.23 49.23 35.41 2.1 29

5967(4) 895.3433(4) 873.9486(3) 0.549(2) 14.3(2) [28.6] [20.3] [5.1] 529.01 49.26 35.44 1.4 20

Errors in parentheses are expressed in units of the last digit. Centrifugal distortion constants were fixed at the values of the parent species. Standard deviation of the fit. Number of transitions in the fit.

Table 5 Comparing the rotational constants of the three isomers of DFM-DFE calculated at different levels of theory to those of experimental ones. Rotational constants (MHz) Isomer

I

A, B, C II

III

Exp. MP2/6-311++G(d,p) MP2/6-311++G(2df,2pd) MP2/6-311++G(3df,3pd) MP2/aug-cc-pVDZ B97D/6-311++G(d, p) xB97XD/6-311++G(d,p) xB97XD/aug-cc-pVDZ M06-2X/6-311++G(d,p) B3LYP/6-311++G(d,p) B3LYP-D3(BJ)/6-311++G(d,p) B3LYP-D3(BJ)/def2-TZVPP B2PLYP/6-311++G(d,p)

4377.6, 1053.7, 990.4 4246, 1114, 1026 4481, 1088, 1035 4457, 1092, 1033 4296, 1072, 1018 4037, 1078, 1003 4378, 1055, 998 4370, 1026, 977 4544, 1184, 1123 4141, 1038, 956 4166, 1123, 1040 4280, 1062, 998 4200, 1090, 1002

4255.1, 1009.0, 968.7 4313, 1027, 990 4277, 1041, 1000 4233, 1049, 1004 4050, 1042, 992 4025, 1021, 973 4093, 1037, 986 3993, 1020, 966 4555, 1128, 1096 4103, 974, 932 4106, 1064, 1013 4104, 1019, 972 4186, 1013, 971

5971.8, 900.9, 879.2 6027, 924, 898 5992, 939, 914 5930, 938, 915 5649, 925, 904 5517, 899, 884 5734, 908, 890 5557, 888, 874 6300, 994, 961 5770, 865, 847 5747, 934, 915 5770, 901, 882 5922, 902, 880

Fig. 3. The selected 505 404 transition for isomers I-III measured with carrier gas Ar (upper) and He (lower).

but results in large differences between experimental and theoretical rotational constants for isomers II (3.1%, 2.8% and 1.9%) and III (4.0%, 0.8% and 1.2%). Calculations at the MP2 level with 6-311++G (2df,2pd) and 6-311++G(3df,3pd) basis set improve the agreement of the theoretical rotational constants with the experimental values. Overall, the results of MP2/6-311++G(3df,3pd) level of

calculations for isomers I, II and III match the corresponding experimental values. The configurations of the three observed isomers of DFM-DFE are presented in Fig. 1, where the atomic numbering and principal axes of inertia are also provided. The determined planar moments of inertia of parent and the 13C isotopologues provide additional structural insight indicating that both isomers II and III have a plane of symmetry (see Fig. S1). As shown in Fig. 1, both DFM and DFE act as weak proton donors and weak proton acceptors in all the three observed isomers, which are stabilized via a net of three CAH


FAC WHBs. For isomer III, the methyl group is not involved in the intermolecular WHBs. The barrier to the internal rotation of ACH3 group is calculated to be 1244 cm1 (Fig. S2), in agreement with the fact that no splitting due to the internal rotation of methyl group was observed. To experimentally confirm the global minimum and the relative stability of the three isomers, the intensities of several selected transitions for each isomer were compared with those measured in argon because it is well known that conformational relaxation of higher energy species to lower energy one more easily occurs in Ar [46]. As shown in Fig. 3, the selected transitions of the three isomers have very different intensities in Ar and in He: lines of isomers I and II become almost undetectable in Ar whereas they have intense signals in He. Comparatively, the signal of isomer III is almost twice intense in Ar than that in He. The measurements evidence that isomer III should be the global minimum. The intensity measurements in He also allow estimating the relative abundance of the three isomers in the supersonic expansion as NI/NII/NIII  5/2/6 [47].

36

T. Lu et al. / Journal of Molecular Spectroscopy 357 (2019) 32–37

3.4. Molecular structure According to the experimental rotational constants reported in Tables 2–4, the coordinates of the three substituted carbon atoms of each isomer were calculated by using the Kraitchman’s method [48]. The obtained results are reported in Table S5 and are compared with the ab initio values (re, MP2/6-311++G(3df,3pd) level). Based on the four sets of rotational constants for each isomer, partial r0 [49] structures of all three observed isomers were calculated independently by fitting several structural parameters to minimize the differences between the theoretical rotational constants and the experimental ones. The starting structures of two monomers in all the three observed isomers were fixed at their ab initio (MP2/6-311++G(3df,3pd)) geometries (see Tables S6–S8 in the Supplementary Material). The fitted parameters are provided in Table 6 and compared with the re structures from MP2/6-311+ +G(3df,3pd) level of theory. The derived WHB lengths and the relevant angles from the partial r0 structures of these three isomers are also reported in Table 6. These values are very close to the theoretical ones. The determined parameters of CAH


CAF linkages are comparable to those for (CH2F2)2 [25], (CH3CHF2)2 [28] and (CF3CH2F)2 [29].

3.5. Weak hydrogen bonds In order to quantify the CAH


FAC interactions involved in the observed isomers, Bader’s quantum theory of atoms in molecules (QTAIM) analysis [50] was carried out by using the Multiwfn program [51]. The results are displayed in Fig. S3. Bond critical points (BCPs) and the corresponding bond paths of the WHBs contributing to the stabilization of the isomers I, II, and III were identified, indicating that three CAH


FAC WHBs account for the stabilization of Table 6 Experimental (rs and r0) and theoretical (re) structural parameters of the three observed isomers. rs I r(C2C9) (Å) 3.729(5)a \C1C2C9 (°) 91.2(5) Derived WHB parameters r(H5F13) (Å) r(H6F12) (Å) r(F8H10) (Å) \F8H10C9 (°) \F12H6C2 (°) \F13H5C1 (°) II r(C2C9) (Å) 3.758(4) \C1C2C9 (°) 93.3(5) Derived WHB parameters r(H3F13) (Å) r(F7H11) (Å) r(F8H10) (Å) \F7H11C9 (°) \F8H10C9 (°) \F13H3C1 (°) III r(C2C9) (Å) 3.532(6) \C1C2C9 (°) 174(5) Derived WHB parameters r(H6F12) (Å) r(F8H10) (Å) r(F7H11) (Å) \F8H10C9 (°) \F7H11C9 (°) \F12H6C2 (°) a b

r0

r eb

3.753(4) 90.9(4)

3.662 87.5

2.754(4) 2.642(4) 2.502(4) 119.4(4) 114.3(4) 145.6(4)

2.590 2.602 2.463 117.8 110.4 147.0

3.7827(3) 93.8(1)

3.6777 93.5

2.4865(3) 2.7474(3) 2.7474(3) 117.4(1) 117.4(1) 143.6(1)

2.4865 2.6097 2.6097 113.9 113.9 143.6

3.545(2) 173.0(3)

3.464 172.6

2.609(2) 2.724(2) 2.724(2) 109.4(3) 109.4(3) 112.1(3)

2.536 2.638 2.638 109.5 109.5 111.7

Errors in parentheses are expressed in units of the last digit. Geometry calculated at the MP2/6-311++G(3df,3pd) level of theory.

Table 7 The values of interaction energy (kJ mol1) for CH


FC interactions identified in isomers I, II and III using the QTAIM analyses. BCPs No.

I

II

III

1 2 3 Sum

4.8 5.3 8.8 18.9

5.9 5.9 6.6 18.4

7.4 5.9 5.9 19.2

Table 8 Energy decomposition analysis calculated at the SAPT2+3/aug-cc-pVDZ-RI level of theory for the three observed isomers of DFM-DFE in comparison with the observed isomers of (CH3CHF2)2, (CH2F2)2 and (H2O)2 (all values are given in kJ mol1). Cluster

Electrostatics

Induction

Dispersion

Exchange

Total

I II III (CH2F2)2 (CH3CHF2)2 I (CH3CHF2)2 II (H2O)2

15.6 15.0 15.5 13.9 16.2 15.2 34.3

2.1 2.0 1.9 2.1 2.2 2.3 10.2

9.7 8.9 8.8 10.0 10.3 10.3 9.4

12.0 10.7 10.9 13.9 12.3 12.2 35.2

15.4 15.2 15.3 12.1 16.4 15.6 18.7

each isomer. The interaction energies of the WHBs can be estimated from the electron potential density, V(r), at the related BCPs through E = 0.5 V(r) [52]. The results are given in Table 7. The interaction energies of the WHBs are estimated within 18–20 kJ mol1. The strength of a single CAH


FAC WHB ranges from 4.8 to 8.8 kJ mol1. The total interaction energies are close to each other, giving the same sequence of relative stability as that suggested by relative intensity measurements. To quantitatively characterize the nature of the WHBs in the three observed isomers, an energy decomposition analysis based on symmetry-adapted perturbation theory (SAPT) [53,54] was performed by using the PSI4 program package [55] at the SAPT2 + 3/aug-cc-pVDZ-RI level of theory. The same level of calculations for (H2O)2, (CH2F2)2 and (CH3CHF2)2 were also performed and provided in Table 8 for comparison. The total interaction energies for isomers I, II, and III of DMF-DFE are between the total interaction energies of (CH2F2)2 and (CH3CHF2)2. For all the three observed isomers, electrostatic and dispersion interactions are the dominant attractive terms whereas electrostatic, induction and dispersion interactions primarily contribute to the interaction energies of (H2O)2 in which the OAH


O hydrogen bond is formed. 4. Conclusions The hetero-dimer of CH2F2 and CH3CHF2 was investigated by pulsed-jet Fourier transform microwave spectroscopy and quantum chemical calculations. Three isomers, in which the subunits are held together via a network of three CAH


FAC interactions, were identified in the jet expansion. The rotational spectroscopic investigations to the parent and 13C isotopologues allow precise structural determination of all three isomers. The relative abundances of the three isomers were estimated by the relative intensity measurements in the pulsed jet. QTAIM and SAPT analyses provide further understanding of the nature of the non-covalent interactions. Acknowledgements This work was supported by Chongqing University under the program of the Foundation of 100 Young, the Fundamental Research Funds for the Central Universities (Grant Nos. 106112017CDJQJ228807 and 10611CDJXZ238826), National Natu-

T. Lu et al. / Journal of Molecular Spectroscopy 357 (2019) 32–37

ral Science Foundation of China (No. 21703021), Fundamental and Frontier Research Fund of Chongqing (Grant Nos. cstc2017jcyjA1503 and cstc2018jcyjA2875), and Venture & Innovation Support Program for Chongqing Overseas Returns (No. cx2018064). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.jms.2019.02.002. References [1] M. Nishio, Y. Umezawa, J. Fantini, M.S. Weiss, P. Chakrabarti, Phys. Chem. Chem. Phys. 16 (2014) 12648–12683. [2] J.M. Lehn, Angew. Chem. Int. Ed. 29 (1990) 1304–1319. [3] R.Y. Zhang, A. Khalizov, L. Wang, M. Hu, W. Xu, Chem. Rev. 112 (2011) 1957– 2011. [4] T. Steiner, Angew. Chem. Int. Ed. 41 (2002) 48–76. [5] S.N. Delanoye, W.A. Herrebout, B.J. van der Veken, J. Am. Chem. Soc. 124 (2002) (1855) 11854–11855. [6] J.P. Toennies, A.F. Vilesov, Angew. Chem. Int. Ed. 43 (2004) 2622–2648. [7] K.R. Leopold, G.T. Fraser, S.E. Novick, W. Klemperer, Chem. Rev. 94 (1994) 1807–1827. [8] M. Becucci, S. Melandri, Chem. Rev. 116 (2016) 5014–5037. [9] W. Caminati, J.-U. Grabow, Advancements in microwave spectroscopy, in: J. Lanne (Ed.), Frontiers and Advances in Molecular Spectroscopy, Elsevier, Amsterdam, 2018, pp. 569–598 (Ch. 17). [10] Q. Gou, G. Feng, L. Evangelisti, M. Vallejo-López, A. Lesarri, E.J. Cocinero, W. Caminati, Phys. Chem. Chem. Phys. 15 (2013) 6714–6718. [11] G. Feng, Q. Gou, L. Evangelisti, M. Vallejo-López, A. Lesarri, E.J. Cocinero, W. Caminati, Phys. Chem. Chem. Phys. 16 (2014) 12261–12265. [12] G. Feng, L. Evangelisti, L.B. Favero, J.-U. Grabow, Z.N. Xia, W. Caminati, Phys. Chem. Chem. Phys. 13 (2011) 14092–14096. [13] W. Caminati, S. Melandri, I. Rossi, P.G. Favero, J. Am. Chem. Soc. 121 (1999) 10098–10101. [14] W. Caminati, S. Melandri, A. Maris, P. Ottaviani, Angew. Chem. Int. Ed. 45 (2006) 2438–2442. [15] B.J. Bills, L.F. Elmuti, A.J. Sanders, A.L. Steber, R.A. Peebles, S.A. Peebles, P. Groner, J.L. Neill, M.T. Muckle, B.H. Pate, J. Mol. Spectrosc. 268 (2011) 7–15. [16] L. Evangelisti, G. Feng, P. Écija, E.J. Cocinero, F. Castano, W. Caminati, Angew. Chem. Int. Ed. 50 (2011) 7807–7810. [17] G. Feng, L. Evangelisti, N. Gasparini, W. Caminati, Chem. -Eur. J. 18 (2012) 1364–1368. [18] L. Evangelisti, G. Feng, Q. Gou, J.-U. Grabow, W. Caminati, J. Phys. Chem. A 118 (2014) 579–582. [19] W. Caminati, L. Evangelisti, G. Feng, B.M. Giuliano, Q. Gou, S. Melandri, J.U. Grabow, Phys. Chem. Chem. Phys. 18 (2016) 17851–17855. [20] Q. Gou, G. Feng, L. Evangelisti, M. Vallejo-López, L. Spada, A. Lesarri, E.J. Cocinero, W. Caminati, Chem.-Eur. J. 21 (2015) 4148–4152. [21] Q. Gou, L. Spada, E.J. Cocinero, W. Caminati, J. Phys. Chem. Lett. 5 (2014) 1591– 1595. [22] Q. Gou, G. Feng, L. Evangelisti, W. Caminati, Angew. Chem. Int. Ed. 52 (2013) (1891) 11888–11891. [23] Q. Gou, L. Spada, Y. Geboes, W.A. Herrebout, S. Melandri, W. Caminati, Phys. Chem. Chem. Phys. 17 (2015) 7694–7698. [24] L. Spada, Q. Gou, Y. Geboes, W.A. Herrebout, S. Melandri, W. Caminati, J. Phys. Chem. A 120 (2016) 4939–4943. [25] W. Caminati, S. Melandri, P. Moreschini, P.G. Favero, Angew. Chem. Int. Ed. 38 (1999) 2924–2925. [26] S. Blanco, S. Melandri, P. Ottaviani, W. Caminati, J. Am. Chem. Soc. 129 (2007) 2700–2703.

37

[27] G. Feng, L. Evangelisti, I. Cacelli, L. Carbonaro, G. Prampolini, W. Caminati, Chem. Commun. 50 (2014) 171–173. [28] J.H. Chen, Y. Zheng, J. Wang, G. Feng, Z.N. Xia, Q. Gou, J. Chem. Phys. 147 (2017) 094301. [29] X.L. Li, Y. Zheng, J.H. Chen, J.-U. Grabow, Q. Gou, Z.N. Xia, G. Feng, J. Phys. Chem. A 121 (2017) 7876–7881. [30] C.L. Christenholz, D.A. Obenchain, R.A. Peebles, S.A. Peebles, J. Phys. Chem. A 118 (2014) 1610–1616. [31] Y. Tatamitani, K. Yamanou, H. Kanno, T. Ogata, J. Mol. Spectrosc. 242 (2007) 150–155. [32] T. Lu, J.H. Chen, J.Q. Zhang, Q. Gou, Z.N. Xia, G. Feng, ChemPhysChem 19 (2018) 2655–2661. [33] W. Caminati, J.C. López, J.L. Alonso, J.-U. Grabow, Angew. Chem. Int. Ed. 44 (2005) 3840–3844. [34] L. Spada, Q. Gou, S. Tang, W. Caminati, New J. Chem. 39 (2015) 2296–2299. [35] Q. Gou, L. Spada, M. Vallejo-López, Z. Kisiel, W. Caminati, Chem. Asian J. 9 (2014) 1032–1038. [36] C.L. Christenholz, D.A. Obenchain, S.A. Peebles, R.A. Peebles, J. Mol. Spectrosc. 280 (2012) 61–67. [37] J.-U. Grabow, W. Stahl, H.A. Dreizler, Rev. Sci. Instrum. 67 (1996) 4072–4084. [38] T.J. Balle, W.H. Flygare, Rev. Sci. Instrum. 52 (1981) 33–45. [39] J.-U. Grabow, Q. Gou, G. Feng, 72nd International Symposium on Molecular Spectroscopy, TH03 Champaign-Urbana, 2017. [40] J.-U. Grabow, Habilitationsschrift, Universität Hannover, Hannover, 2004. Program available at <~lgpca/spectroscopy/ftmw" xlink:type="simple" id="ir010">http://www.pci.uni-hannover.de/~lgpca/spectroscopy/ftmw>. [41] S.F. Boys, F. Bernardi, Mol. Phys. 19 (1970) 553–566. [42] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, G.A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A.V. Marenich, J. Bloino, B.G. Janesko, R. Gomperts, B. Mennucci, H.P. Hratchian, J.V. Ortiz, A.F. Izmaylov, J.L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V.G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M.J. Bearpark, J.J. Heyd, E.N. Brothers, K.N. Kudin, V.N. Staroverov, T.A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A.P. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, J.M. Millam, M. Klene, C. Adamo, R. Cammi, J.W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J.B. Foresman, D.J. Fox, Gaussian 16, Revision A.03, Gaussian, Inc., Wallingford, CT, 2016. [43] R.M. Villamanan, W.D. Chen, G. Wlodarczak, J. Demaison, A.G. Lesarri, J.C. Lopez, J.L. Alonso, J. Mol. Spectrosc. 171 (1995) 223–247. [44] H.M. Pickett, J. Mol. Spectrosc. 148 (1991) 371–377. [45] Vibrational Spectra and Structure vol. 6 (1977) 1–89. [46] R.S. Ruoff, T.D. Klots, T. Emilsson, H.S. Gutowsky, J. Chem. Phys. 93 (1990) 3142–3150. [47] W. Caminati, J.C. López, S. Blanco, S. Mata, J.L. Alonso, Phys. Chem. Chem. Phys. 12 (2010) 10230–10234. [48] J. Kraitchman, Am. J. Phys. 21 (1953) 17–24. [49] Z. Kisiel, J. Mol. Spectrosc. 218 (2003) 58–67. [50] R.F.W. Bader, Chem. Rev. 91 (1991) 893–928. [51] T. Lu, F.W. Chen, J. Comput. Chem. 33 (2012) 580–592. [52] I. Mata, I. Alkorta, E. Espinosa, E. Molins, Chem. Phys. Lett. 507 (2011) 185–189. [53] B. Jeziorski, R. Moszynski, K. Szalewicz, Chem. Rev. 94 (1994) 1887–1930. [54] T.M. Parker, L.A. Burns, R.M. Parrish, A.G. Ryno, C. David Sherrill, J. Chem. Phys. 140 (2014) 094106. [55] R.M. Parrish, L.A. Burns, D.G.A. Smith, A.C. Simmonett, A.E. DePrince III, E.G. Hohenstein, U. Bozkaya, A.Yu. Sokolov, R. Di Remigio, R.M. Richard, J.F. Gonthier, A.M. James, H.R. McAlexander, A. Kumar, M. Saitow, X. Wang, B.P. Pritchard, P. Verma, H.F. Schaefer III, K. Patkowski, R.A. King, E.F. Valeev, F.A. Evangelista, J.M. Turney, T.D. Crawford, C.D. Sherrill, J. Chem. Theory Comput. 13 (2017) 3185–3197.