T. M. Petrova

IR spectroscopy of water vapor confined in nanoporous silica aerogel.

The absorption spectrum of the water vapor, confined in the nanoporous silica aerogel, was measured within 5000-5600 cm(-1) with the IFS 125 HR Fourier spectrometer. It has been shown, that tight confinement of the molecules by the nanoporous size leads to the strong lines broadening and shift. For water vapor lines, the HWHM of confined molecules are on the average 23 times larger than those for free molecules. The shift values are in the range from -0.03 cm(-1) to 0.09 cm(-1). Some spectral lines have negative shift. The data on the half-widths and center shifts for some strongest H(2)O lines have been presented.

Water vapor continuum absorption in near-IR atmospheric windows

The near-infrared water vapor absorption is measured in the 2000–8000 cm−1 spectral region. Spectra were recorded using an IFS 125 HR Fourier spectrometer at a temperature of 287 K and a spectral resolution of 0.03 cm−1. The water vapor continuum absorption spectrum is retrieved using the known absorption in the 2500 cm−1 region as a reference point. It is shown that the continuum absorptions in four windows differ by no more than 20% under investigation conditions. This contradicts the MT_CKD continuum model, which predicts a much stronger variability of the continuum in these windows.

A Fourier-spectrometer with a 30-m base-length multipass cell for the study of weak absorption spectra of atmospheric gases

The design and specifications of the experimental set-up, consisting of an IFS-125 HR Fourier spectrometer and a 30-m base length multipass cell with the White optical system, are described. An optical path length of more than 600 m is attained. Results of measurement of atmospheric air spectra with a spectral resolution of 2 × 10−2 cm−1 and a sensitivity of less than 10−8 cm−1 are presented. It is shown that the complex reliably detects very weak absorption spectra of atmospheric molecules, including their isotopic modifications.

Spectroscopic nanoporometry of aerogel

The sizes of aerogel nanopores from the measured broadening of rotational-vibrational CO lines caused by collisions with nanopore walls have been determined. It has been shown that the sizes of nanopores with a diameter of 15–25 nm can be reliably assessed from the half-widths of spectral lines measured on a high-resolution Fourier spectrometer and agree well with the experimental data found from the low-temperature adsorption of nitrogen.

Observation of a forbidden vibrational absorption band of H2 in nanoporous aerogel

Room-temperature absorption spectra of H2 in nanoporous aerogel with a pore diameter of ∼20 nm have been studied on a Fourier spectrometer in the spectral range of 4000–4800 cm−1. Absorption at the forbidden transitions of the 0–1 vibrational band has been observed. The recorded spectra of H2 in aerogel have been compared with the spectra of free high-pressure H2.

CO2 absorption in band wings in near IR

The CO2 absorption was measured in the 7000 and 8000 cm–1 regions. The absorption coefficients were calculated using the asymptotic line wing shape theory. Line shape parameters were found from fitting to experimental data. The calculation results agree well with the measurement data. According to the line wing theory, the absorption in the band wings is caused by the wings of strong lines of an adjacent band. Within these assumptions, experimental and calculated data on the CO2 absorption coefficient in the band wings in the 7000 and 8000 cm–1 regions can provide information on the line shape at frequency detuning from several tens to several hundreds of half-widths. The results support the hypothesis that line shape parameters in the line wings related to transitions with the same initial state are close to each other. Deviations from a Lorentzian profile are found for some CO2 bands and turn out different for the wings of different bands

Experimental study by the IR spectroscopy method of the interaction between ethylene and nanopores of various densities

The combination vibrational bands ν5 + ν9 and ν1 + ν11 of ethylene absorption adsorbed by silica aerogel nanopores of different densities have been studied for the first time in the 5700- to 6300-cm−1 spectral region. The conducted measurements show significant differences between the spectra of ethylene in aerogels and ethylene in the gas phase, which consist of the change of the absorption band shapes, the shift of the band frequency, and the increase of the absorption intensity. It was concluded that in the studied pressure range of 88–952 mbar, the adsorbed ethylene is in the same structural state.

Spectrometric complex for investigation of spectra of selective and nonselective gas absorption in a wide spectral range

A spectrometric complex for investigation of absorption spectra in a wide spectral range (from 500 to 40000 cm–1) with high threshold sensitivity to the absorption coefficient is presented. The complex was designed at the Institute of Atmospheric Optics, SB RAS. The description of the cell and optical scheme is given, as well as specifications of the complex as compared to other world analogues. Results of the complex use for study spectra of selective and nonselective absorption of molecular gases and recording absorption spectra of molecules confined in optically transparent nanoporous structures are considered.

Fourier spectroscopy of water vapor in the volume of aerogel nanopores. Part 1. Measurements and calculations

Broadening and shifting of absorption lines of water vapor confined inside aerogel nanopores have been studied with the help of a IFS 125 HR Fourier spectrometer in the region 5000–5600 cm−1. It is shown that strong spatial limitation of molecular movement results in significant broadening and shifting of spectral lines. A semiempirical model for description of the form of absorption line contours for H2O molecules confined inside aerogel nanopores, taking account of the dependence of spectral line half-width on rotational quantum numbers, is presented for the first time. Values of spectral line half-widths found experimentally and theoretically are in good agreement.