Study of the ν1 band shape of the H2O⋯HF, H2O⋯DF, and H2O⋯HCl complexes in the gas phase

Abstract

The band shape of the upsilon1 hydrogen fluoride stretch in H20...HF and H2O...DF complexes was studied in the gas phase. The spectra of H2O/HF mixtures at 293 K in cells 20 and 1200 cm long were recorded in the range 4200-3000 cm(-1) at a resolution of 0.2-0.02 cm(-1). The spectra of the 1 : 1 complex in the region of the upsilon1(HF) absorption band were obtained by subtracting the calculated spectra of free H2O and HF molecules from the experimental spectra. The asymmetric upsilon1 band of H2O...HF has a low-frequency head, an extended high-frequency wing, and a characteristic vibrational structure. The upsilon1 band shape was reconstructed nonempirically as a superposition of rovibrational bands of the upsilon1 (HF) fundamental transition and hot transitions from excited states of low-frequency modes. The reconstruction was based on an ab initio calculation of the potential energy and dipole moment surfaces and subsequent variational multidimensional anharmonic calculations of the vibrational energy levels, the frequencies and intensities of the transitions considered, and the rotational constants. The calculated spectrum reproduces the structure of the experimental spectrum, in particular, the relative intensities of the peaks. However, the assignment of spectral features differs from that generally accepted. The central, most intense, peak is associated with the transition from the ground state, while the lowest-frequency peak with the P branch head of transition from the upsilon6 (B2) = 1 state. This leads to a value of 3633.8 cm(-1) for the upsilon1 (HF) stretch frequency of H2O...HF, which is higher than the commonly adopted value of 3608 cm(-1). Similar calculations of H2O...DF predict a value of 2689 cm(-1) for the upsilon1(DF) stretch and a less structured band shape. On formation of a 1 : 1 complex with water the frequency is shifted by -331.8 cm(-1) and -229.4 cm(-1) and the intensity is increased by a factor of 3.87 and 3.51 for HF and DF, respectively. Similar calculations of H2O...HCl predicted a value of 2726.5 cm(-1) for the upsilon1 fundamental, a lower frequency for the hot transition from the upsilon6 (B2) = 1 excited state, and a upsilon1(HCl) band shape in agreement with the results of recent low-temperature experiments.

Comparative analysis of the H–F stretching band in absorption spectra of gas-phase complexes of HF with water, dimethyl ether, and acetone

“…The infrared absorption spectra of mixtures H 2 O/HF [41,42], (CH 3 ) 2 O/HF [43] and mixtures of HF or DF and normal and deuterated acetone were recorded with Bruker IFS-113v and Bruker IFS-120 HR vacuum Fourier spectrometers in the range of 4000-3400, 4200-2800, and 3900-3200 cm -1 , respectively, at a resolution of 0.02-0.2 cm -1 . The band shape of the H-F stretching vibration in the H 2 OÁ Á ÁHF complex was obtained by subtracting the calculated spectra of free H 2 O and HF molecules from the experimental spectrum of H 2 O/HF mixture at room temperature.…”

“…The number of grid points, at which the potential energy and dipole moment components were computed ab initio, was sufficiently large to ensure a required accuracy of the calculated energy levels and transition frequencies and intensities. Other details of computational procedures used in the calculations were reported in [41][42][43].…”

“…The electronic structure and equilibrium geometry of complexes of HF with water [41,42], DME [43], and acetone were calculated using the GAMESS [44] and GAUSSIAN 03 [36] packages in the approximations MP2/TZV++(2df,2p) (complex with water), and MP2/6-311++G(2d,2p) (complexes with DME and acetone) with corrections for the basis set superposition error. The approximations adopted in these calculations are sufficiently accurate.…”

“…For example, it was shown in [40] that the inclusion of one intramolecular degree of freedom in the calculation of a van der Waals complex containing a linear molecule and a rare-gas atom or the H 2 molecule allows one to reproduce the transition frequencies and line intensities in the observed infrared spectra. In our recent studies [41][42][43] the absorption spectra of complexes H 2 OÁ Á ÁHF and (CH 3 ) 2 OÁ Á ÁHF were recorded at different temperatures in the region of the m 1 (H-F) band at a high resolution.…”

Microwave study of the submillimeter spectrum of the H2O⋯HF dimer

“…We feel that it makes sense to publish a translation of our original preprint without updating it, because the main features of the work remain the same. However we present references [29][30][31][32][33] to the most recent work on this molecular complex, which shows the growing interest in this complex from both theoretical and experimental points of view. In particular, from Ref.…”