B. A. Voronin

Molecular line lists for modelling the opacity of cool stars

The behaviour of cool stars is largely governed by molecular absorptions in their outer atmospheres. At the temperatures involved (1000–4000 K), the number of transitions involved can be vast. The underlying physics of the problem is outlined and the status attempts to address the demands of stellar models discussed. Progress on calculations of line lists for stellar models at UCL is described. Specific examples of involving water, HCN/HNC, C3, and HDO are given. Outstanding needs are summarized.

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.

Self- and air-broadening coefficients of HD16O spectral lines

We present the line broadening and self-broadening coefficients of the water isotopologue HD16O and study their dependence on quantum numbers up to J = 50 for P-, Q-, and R-branches. Three calculation techniques have been used: the analytical model in the case of known quantum transition identification in normal modes; the JJ′ dependence in the case when only J and level symmetry are known, and the semiempirical calculation technique for 50 ≥ J > 15. The derived regularities for the broadening coefficients of water vapor lines allow accurate calculation of HD16O spectra including millions of weak lines from the VTT line list (Voronin, Tennyson, and Tolchenov).

LED-Based Fourier Transform Spectroscopy: the HD16O Absorption Spectrum in the Range of 11200–12400 cm−1

The vibrational—rotational spectrum of the HD16O molecule is studied within the range of 11200−12400 cm−1. The spectrum is recorded by an IFS-125M Fourier spectrometer with a resolution of 0.05 cm−1. The measurements are performed using a multipass White cell. A light-emitting diode is used as a radiation source. The signal-to-noise ratio was about 104. The centers, intensities, and half-widths of the spectral lines are determined by fitting to the experimental data by the least-squares method. A linelist containing more than 1500 lines is created. The results obtained are compared with the experimental data of other authors.

Effective potential energy surface of HD16O for calculation of highly excited states of nν3 and ν1 + nν3 types

A new spectroscopically determined potential energy surface (PES) for HD16O is presented, and rotational-vibrational transitions are calculated using it for low rotational quantum numbers J ≤ 4. This surface is constructed by adjusting a high-accuracy PES by fitting to experimental energy levels of nν3 and ν1 + nν3 types. Seven hundred and forty rotational levels with energies up to 25600 cm−1 and J ≤ 8 were used for the refinement. To improve the extrapolation properties of the empirical PES, the fitting was applied to experimental and ab initio energy levels.

H218O spectrum between 13000 and 15500 cm-1

The H218O spectrum has been recently investigated between 11,300 - 13,600 cm-1 covering the 3v plus (delta) spectral region where v is the quantum of the stretching vibration and (delta) is the quantum of the bending vibration. We present here the study of the 4v and 4v plus (delta) region between 13,000 and 15,500 cm-1. Spectra of 18O enriched water vapor have been recorded by means of Fourier-transform spectroscopy. The experimental details have been discussed. The experimental conditions are given.

Self-Broadening and Carbon-Dioxide Broadening of Lines of the H2S Molecule

Carbon-dioxide-broadening coefficients and self-broadening coefficients of lines of the main isotopic modification of Н2S are estimated on the basis of literature data. The J′-dependences of the above line-profile parameters of the hydrogen-sulfide molecule are examined. In the case of CO2 broadening, the half-widths of lines are calculated by a semiempirical method based on a parametric modification of the impact semiclassical model; the model parameters were determined from the fit to experimental data.

Calculations of air-, carbon dioxide and self-broadening coefficients of Н2S lines

Estimations of self-broadening, air-broadening and CO2-broadening coefficients of the main isotopic modification of H2S are performed. The result is presented as formulae describing the dependence of self-broadening, CO2- broadening and air-broadening coefficients on rotational quantum numbers of the lower state of a transition. The comparisons of our estimated self-broadening coefficients values with those from the HITRAN and GEISA databases are presented.

Reanalysis of water-vapor high-resolution spectrum in 13200- to 16500-cm-1 region

The new analysis of water vapor high resolution spectra in 13200 - 16500 cm -1 region has been done using conventional scheme of the effective Hamiltonians in the Pade-Borel approximants representation. About 30 percent of new energy levels has been derived after the spectrum identification including the highest ever observed (0 10 0) [7 0 7] level. An alternative method of the spectrum identification using recent ab initio and variational calculations is discussed.