L. N. Sinitsa

The laser spectroscopy of highly excited vibrational states of HD16O

Abstract The absorption spectra of HD 16 O were recorded using a F 2 + :LiF color center intracavity laser spectrometer in the 0.9-μm region and an optoacoustic dye laser spectrometer in the 0.59-μm spectral region. Energy levels and rotational and centrifugal distortion constants of the (003) and (005) states were determined. Improved sets of vibrational and vibration-rotation constants have been obtained by fitting all available data for the energy levels of HDO.

Intracavity laser spectroscopy of high-temperature water vapour in the range 9390–9450 cm−1

The absorption spectra of water vapour were studied in the range 9390–9450 cm−1 using an ICL-spectrometer based on a Nd-glass laser with a spectral resolution of 0.036 cm−1 and threshold sensitivity to absorption of 10−8 cm−1. A high temperature absorption cell was used to record the H2O spectra at temperatures of 300 to 800 K and a Multyplaz-2500 plasma source enabled water vapour temperatures up to 3000 K. The recorded spectra are very dense over the wavenumber region investigated, showing in addition to the water lines, absorption of the OH molecule. More than 250 absorption lines were detected in the high-temperature spectra of water vapour. Lines determined by transitions to the second hexade of H2O from the ground vibration state as well as hot bands were assigned. The temperature of the flame and the concentration of the OH molecules were also determined using the OH transitions in the ground electronic state.

High-sensitive Fourier-transform spectroscopy with short-base multipass absorption cells

A high-sensitive spectrometer operating in the range 20000–9000 cm−1 with an absorption sensitivity of 1 × 10−8 cm−1 and a spectral resolution of 0.05 cm−1, based on the Bruker IFS-125M Fourier spectrometer with a short multipass cell, is described. The high sensitivity of the spectrometer was gained through the use of the multipass absorption cell (a base length of 60 cm) with a high transmission (the ratio of the collecting mirror diameter to the base length is 1 : 4) and a high intensity light source.The comparison of the recorded spectra with experimental and theoretical water vapor spectra shows that the spectrometer reliably detects absorption lines of natural isotopomers of water. The threshold sensitivity of the spectrometer was found from the signal/noise ratio and recorded water lines of minimal intensities.

Experimental setup for spectrophotometric study of water clusters in nanoporous material

An experimental setup for spectrophotometric study of water clusters in a nanoporous material is described. It can record absorption spectra of porous materials at different temperatures and in different pumping regimes.

Shift of the centers of H2O absorption lines in the region of 1.06 μm

The shift coefficients for the lines of the ν1 + ν2 + ν3 and ν2 + 2ν3 bands of H2O in the region from 9403 to 9413 cm−1 are measured and calculated. The measurements are performed using an intracavity laser spectrometer based on a neodymium laser with a determination error of the line center of 0.003–0.004 cm−1. The Ar, Kr, and Xe noble gases, as well as nitrogen, oxygen, and hydrogen were used as buffer gases. The coefficients of shifts in eight H2O absorption lines induced by oxygen, nitrogen, and atmospheric air pressures fall into the region from −0.004 to −0.069 cm−1/bar. The calculations are performed by a semiempirical method using variational wave functions, which, in contrast to other studies, correctly takes into account intramolecular interactions. The calculated values agree satisfactorily with experimental data.

Dynamic registration of D216O absorption spectrum in silica aerogel

Absorption spectra of the gas phase and adsorbed D2О in the silica aerogel with nanoscale pores were investigated in 3700–5400 cm−1 range using dynamic registration with Fourier Transform spectrometer IFS-125M. Two types of sample with pores of 60 nm wide – the nitrogen gas-treated and untreated aerogels – were examined. The surface treatment of the sample changes noticeably the broadband absorption of adsorbed water. Spectrum of D2O in the pores differs from the spectrum of bulk water as for bandwidth so for band maximum. It was found that treatment of the pores by dry nitrogen leads to increasing hydrophilic properties of the material and to change water band contour. The D2О line widths in both the aerogels exceed those of free monomer in 1.1–3 times at the same pressure. Calculations of self-broadening coefficients of the D2O lines were performed using semi-empirical method based on the impact theory of broadening and includes the correction factors. The calculated results well agree with experimental data. Greater differences were found for the shift of the line centre. The D2O line shifts in the treated pores significantly exceed line shifts in the untreated pores. For some lines, these shifts have the opposite sign indicating complex nature of the molecule–wall interaction.

Spectral system for measuring gaseous atmospheric components with a fiber-optic tracking system, and certain analysis results of atmospheric spectra

A spectral system for measuring atmospheric gaseous components based on a Brucker IFS 125M Fourier Transform Spectrometer (FTS) with a fiber-optic tracker is described. Experimental results on the determination of CO2 and H2O contents in the atmosphere above Tomsk from the analysis of atmospheric transmission spectra of solar radiation, recorded with the FTS, are presented. The atmospheric transmission spectra are compared for solar zenith angles of 34° and 78°, which show a significant quantity of oxygen collision complexes in the surface air layer.

The absorption spectrum of H218O in the range 13400–14460 cm−1

Using a Fourier-transform spectrometer, we have measured the absorption spectrum of H218O vapor in the range 13400–14460 cm−1 at room temperature with a resolution of 0.03 cm−1 and a threshold sensitivity in absorption of 10−6 cm−1. With a multipass cell, the volume of which was 3 L and the base of which was 25 cm, a length of the absorbing layer of 10 m has been achieved. A high signal-to-noise ratio, on the order of 1000, has allowed us to detect about 700 lines of the H218O molecule, the intensities of which were as low as 10−25 cm/molecule, at 296 K. The observed lines have been attributed to eleven vibrational-rotational bands of the molecule.

Influence of the interference between water vapor lines on the atmospheric transmission of near-IR radiation

The influence of the interference between IR spectral lines of water vapor on the atmospheric transmission has been studied. The calculations have shown that, for a relatively low pressure, the influence of the interference on the line shift is small for most water vapor lines. However, this influence can be significant for lines whose upper vibrational-rotational states are in a strong resonance. Thus, a relation exists between intramolecular resonances of different types, which manifest themselves as a result of an abnormally strong vibrational-rotational interaction and interference arising due to collisional distortion of molecular steady states. The interference between lines distorts the Lorentz shape of a line profile and leads to a nonlinear pressure dependence of the line shift and to an increased absorption in the atmospheric microwindows. The influence of the interference for a horizontal path is small: the largest addition is 3% at a frequency of 12414.07 cm−1. For a slant atmospheric path under summer conditions, the line interference contributes 0.5%, and for winter conditions the influence of the interference is about 1.5%. It is concluded that the line interference increases the absorption in the atmospheric microwindows.

Observation of water dimers in nanopores of silicon aerogel

The study of the dynamics of adsorption–desorption of heavy water vapor in nanopores of SiO2 aerogel with pores with a diameter of 50 nm on a high-resolution Fourier spectrometer has revealed absorption by D2O dimers. It has been shown that the difference of the absorption spectrum of heavy water in aerogel from that in liquid D2O is due to the presence of additional absorbing structures—dimers and near-wall water.