**
**EXPERIMENTAL AND THEORETICAL STUDY OF THE *H*_{2}O…HF
COMPLEX IN THE GAS PHASE. COMPLETELY NONEMPIRICAL CALCULATION OF THE n(*HF*)
BAND STRUCTURE.

V.P. BULYCHEV, E.I. GROMOVA, AND K.G. TOKHADZE

The n (*HF*) band profile in *H*_{2}O...HF
hydrogen-bonded complex was studied in the gas phase at T=293 K. The spectra of the *HF/Í*_{2}O
gaseous mixtures were recorded in the 4200-3000 cm^{-1} spectral region with a Bruker 120 FTIR spectrometer at 0.2-0.02 cm^{-1} resolution
using the stainless steel cell (L=20 cm) with sapphire windows. The spectra of *H*_{2}O..HF
complex in the region of the n _{1}(*HF*)
absorption band were obtained by subtracting the calculated spectra of free *H*_{2}O
and *HF* molecules from the experimental spectrum. The n
_{1 }band of the *H*_{2}O…HF complex has an asymmetric shape with
a low-frequency head, an extended high-frequency wing, and the characteristic vibrational
structure. Two variants of reconstruction of the n _{1 }band
shape as a superposition of vibration-rotational bands of the fundamental and hot
transitions were considered. A simplified semiempirical procedure was used in the first
variant. The second variant was based on a nonempirical anharmonic calculation of the
vibrational level energies,the frequencies and intensities of corresponding transitions
and the rotational constants. These parameters were determined by an ab initio SCF MP2 calculation of surfaces of the potential energy and of the
dipole moment and a variational solution of one-, two-, and three-dimensional anharmonic
vibrational problems. The absorption spectrum in the 3720-3600 range, reconstructed with
the use of the nonempirical electrooptical parameters, sufficiently well reproduces the
main characteristics of the experimental spectrum, in particular, the relative intensities
of maxima of the vibrational structure. However, the interpretation of most of the
structural features of the spectrum differs from that assumed in the semiempirical scheme.
Above all, it follows from the results of the nonempirical calculation that the n_{1}=1¬0 transition from the
ground vibrational state should be associated with the central, most intense maximum of
the experimantal spectrum. Allowance for this fact leads to a new value of vibrational
transition frequency n_{1}^{0} in the *H*_{2}O..HF
complex equal to 3635 ñm^{-1}, which is higher than the commonly accepted value
of 3608 ñm^{-1}.

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