K. G. Tokhadze

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

The band shape of the ν1 hydrogen fluoride stretch in H2O⋯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 ν1(HF) absorption band were obtained by subtracting the calculated spectra of free H2O and HF molecules from the experimental spectra. The asymmetric ν1 band of H2O⋯HF has a low-frequency head, an extended high-frequency wing, and a characteristic vibrational structure. The ν1 band shape was reconstructed nonempirically as a superposition of rovibrational bands of the ν1(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 v6(B2) = 1 state. This leads to a value of 3633.8 cm−1 for the ν1(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 ν1(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 ν1 fundamental, a lower frequency for the hot transition from the v6(B2) = 1 excited state, and a ν1(HCl) band shape in agreement with the results of recent low-temperature experiments.

First example of the ABC ν(OH) absorption structure for both gaseous and crystalline phase: infrared studies of dimethylphosphinic acid

Abstract Infrared spectra for both gaseous (4000-1000 cm −1 ) and polycrystalline (4000-400 cm −1 ) samples of dimethylphosphinic acid (CH 3 ) 2 POOH (DMPA) at various temperatures are reported and discussed. The main attention is focused on the hydrogen bond vibrations. For the first time, the characteristic ABC structure of the ν(OH) band, occurring in the spectra of solid samples of strongly hydrogen bonded complexes was observed in the gas phase spectra of DMPA dimers. In spite of different types of aggregates present in the solid state a similar shape of the ν(OH) absorption was found in the crystalline sample spectra. However, an inverse intensity distribution of the ABC subbands was observed. The presented results fully confirm the explanation of the ABC structure as being due to the Fermi resonances between ν(OH) and overtones of the deformation modes 2δ(OH) and 2γ(OH).

High-resolution Fourier-transform IR spectroscopic determination of impurities in silicon tetrafluoride and silane prepared from it

The impurity compositions of silicon tetrafluoride and silane prepared from it have been determined by high-resolution Fourier-transform IR spectroscopy. In the spectra of SiF4 samples differing in purity, we have identified rovibrational bands arising from Si2F6O, SiF3OH, HF, SiF3H, SiF2H2, SiH3F, CH4, CO2, and CO impurities. Their detection limits lie in the range 9 × 10−5 (CO2) to 3 × 10−3 mol % (Si2F6O). In the spectra of SiH4 samples of different purity, we have detected CH4, CO2, SiF3H, SiF2H2, and SiF4 impurities. Their detection limits lie in the range 8 × 10−5 (CO2) to 1 × 10−3 mol % (SiF4).

About origin of Q component on the vibration-rotation band of HF in simple solvents

The evolution of the fundamental νHF absorption in the spectra of HF/Ar, Xe, CO2, CO mixtures at densities varying from dilute gas to liquid has been studied. The spectral region of the HF librational mode has been simultaneously examined. The results show that molecular complexes play the crucial role in the mechanism of formation of the Q component in the spectra of HX in simple solvents.The evolution of the fundamental νHF absorption in the spectra of HF/Ar, Xe, CO2, CO mixtures at densities varying from dilute gas to liquid has been studied. The spectral region of the HF librational mode has been simultaneously examined. The results show that molecular complexes play the crucial role in the mechanism of formation of the Q component in the spectra of HX in simple solvents.

Photolysis of the OC⋯HONO complex in low temperature matrices: Infrared detection and ab initio calculations of nitrosoformic acid, HOC(O)NO

Photochemistry of OC⋯HONO complexes in nitrogen matrices has been investigated using λ>340 nm radiation of a medium pressure mercury arc. Reaction of the OH radicals from HONO photolysis with CO within the nitrogen lattice site has led to formation of trans and cis-HOCO radicals. The HOCO radicals reacted further with NO via two reaction channels yielding trans and cis-HOC(O)NO or HNO+CO2. Comparison of the observed infrared frequencies and isotope shifts (13C, 18O, and 2H) with the computed frequencies confirmed the assignment of the cis and trans conformers of nitrosoformic acid that have been identified for the first time. In matrices with higher CO concentration the complexes between cis-HOC(O)NO molecule and carbon monoxide were also identified.

Experimental and theoretical study of the ν(HF) absorption band structure in the H2O…HF complex

The νHF absorption band shape of the H2O…HF complex is studied in the gas phase at a temperature of 293 K. The spectra of H2O/HF gaseous mixtures in the range 4000–3400 cm−1 are recorded at a resolution of 0.2–0.02 cm−1 with Bruker IFS-113v and Bruker IFS-120 HR vacuum Fourier spectrometers in a 20-cm cell. The spectra of the H2O…HF complex in the region of the ν1(HF) absorption band are obtained by subtracting the calculated spectra of free H2O and HF molecules from the experimental spectrum. The ν1 band of the H2O…HF complex has an asymmetric shape with a low-frequency head, an extended high-frequency wing, and a characteristic vibrational structure. Two approaches are used to calculate the ν1 band shape as a superposition of rovibrational bands of the fundamental and hot transitions involving the low-frequency modes of the complex. The first approach is based on a simplified semiempirical procedure. The second approach relies on a nonempirical anharmonic calculation of the vibrational energy levels, the frequencies and intensities of the corresponding transitions, and the rotational constants. These parameters are obtained by calculating ab initio the potential energy and dipole moment surfaces in the second-order Möller-Plesset approximation and using the variational method to solve one-, two-, and three-dimensional anharmonic vibrational problems. The absorption spectrum of the complex in the range 3600–3720 cm−1, reconstructed using the nonempirical electro-optical parameters, reproduces rather well the main features of the experimental spectrum, including the relative intensities of peaks of the vibrational structure. However, the interpretation of most of the structural features of the spectrum differs from that adopted in the semiempirical scheme. First of all, it follows from the results of nonempirical calculation that the central, most intense, maximum of the experimental spectrum should correspond to the v1=1←0 transition from the ground vibrational state. This fact gives rise to a new value of the vibrational transition frequency ν10 in the H2O…HF complex equal to 3635 cm−1, which is higher than the commonly accepted value of 3608 cm−1.

Infrared matrix isolation spectra of SF6 dimers

Abstract The infrared spectra of 32 SF 6 , 33 SF 6 and 34 SF 6 dimers were studied in argon and nitrogen matrices. The spectra of SF 6 dimers of like and unlike isotopomers were also calculated taking into account the resonance dipole–dipole and dipole-induced dipole interactions between two triply degenerate oscillators. Two absorption bands with site structure are observed for ( 32 SF 6 ) 2 , ( 33 SF 6 ) 2 and ( 34 SF 6 ) 2 in argon; the ν X , Y band is blue shifted and the ν Z band is red shifted from the ν 3 SF 6 band in accordance with calculated spectra. Three and two components of the predicted quadruplets are identified for 32 SF 6 – 34 SF 6 , 32 SF 6 – 33 SF 6 , respectively. In the spectra of (SF 6 ) 2 in nitrogen matrices the splitting of ν X , Y component of the resonance doublet was observed.

Matrix infrared spectra of HONOC2H4 complexes in solid argon

Abstract The complexes formed by trans- and cis-HONO isomers with ethene have been observed and characterized in argon matrices. Five perturbed trans-HONO vibrations and four perturbed cis-HONO vibrations were identified for the complexes formed by the trans and cis isomers, respectively. The strong perturbation of the OH group vibrations of both isomers and the blue shift of the out-of-plane bending vibration of ethene in the trans complex indicate the formation of hydrogen-bonded II complexes. The strength of interaction increases from the cis to the trans isomer.

Infrared studies of the nitrous acid complexes with Xe and N2 in argon, krypton and xenon matrices

Abstract The complexes formed by trans - and cis -HONO isomers with xenon were observed and characterized in argon matrices. The complexes of the two isomers with nitrogen in krypton and xenon matrices were also studied.

Ab initio calculations and matrix infrared spectra of the nitrous acid complexes with HF and HCl

Theoretical studies of the structure and spectral characteristics of the complexes formed by trans- and cis-HONO isomers with hydrogen fluoride and hydrogen chloride were carried out on the electron correlation level with the 6-311++G(2d,2p) basis set. The calculations demonstrate formation of three stable complexes between trans-HONO isomer and HX and five stable complexes between cis-HONO isomer and HX. In the most stable HX···trans-HONO, HX···cis-HONO complexes the HX subunit acts as a proton donor and interacts with an oxygen atom of the OH group which is a proton acceptor. The complexes predicted to be the most stable ones were identified and characterized in argon matrices. Six and five perturbed HONO vibrations of trans-HONO isomer were identified, respectively, for HF···trans-HONO and HCl···trans-HONO complexes whereas two perturbed vibrations of cis-HONO isomer were identified for HF···cis-HONO and HCl···cis-HONO complexes.