Home – Home – Jornals – Atmospheric and Oceanic Optics 2015 number 5

The 45-year period of development of the atmospheric spectroscopy at V.E. Zuev Institute of Atmospheric Optics SB RAN is reviewed.

The algorithm of energy level calculation for symmetric 4–6 atomic molecules was considered. The question of choice of coordinates, of the form of potential energy surface, and methods of solutions of Schrödinger equation were considered. The kinetic energy operator for molecules of AB₄ type in internal mass-independent coordinates was built.

In this review, we discuss the current status of construction and applications of potential energy surfaces (PES) for the problems of high resolution molecular spectroscopy. Examples are given for the usage of PES (basically for triatomic molecules) considering the experience of the authors. Several aspects of analytical and spline approaches of PES construction are considered. These aspects are aimed to ensure the physical correctness of a surface and usually being omitted in most of the papers.

In the present work, the MSF computer code is presented intended for determination of the spectral line parameters by their simultaneous fitting to the several absorption spectra recorded under different conditions. Line positions, intensities, pressure broadening and shift coefficients, and lower state energies of dipole transitions in a molecule can be determinable parameters. Basic concept, algorithm, and capabilities of the MSF computer code are outlined in the paper.

High-sensitive spectrometers, created at IAO SB RAS for studying highly excited states, are described. The spectrometers include a Fourier spectrometer with a multipath absorption cell and spectrometers that use modern methods of highly sensitive laser spectroscopy (intracavity laser spectrometers, spectrometers with a high quality external cavity). Designed spectrometers have a high spectral resolution (0.01…0.001 cm^-1) and high sensitivity to absorption (10^-7 - 3 × 10^-9 cm^-1), which makes them promising for the study of parameters of spectral lines arising from transitions to high-energy vibrational-rotational states. The effects of the vibrational-rotational dynamics related to the chaotic behavior under strong excitation are considered by analyzing spectra of water vapor. They are: an anomalous centrifugal distortion, HEL-resonances in H₂O, the nν₃ highly excited states of the HD¹⁶O, the vibrational dependence of the line contour parameters, and the effect of intramolecular resonances on interference lines.

This paper reports the design of the spectroscopic complex at IAO SB RAS for investigation of the absorption spectra in a wide spectral range (from 500 to 40000 cm^-1) with a high sensitivity. The design of 30 m base length cell and the optical scheme are described, the comparison to the known analogous complexes is considered. The results of the study of selective and nonselsective absorption spectra, as well as spectra of gases confined in nanopores are presented.

A technique for calculation of the electric multipole moments and higher molecular polarizabilities is described. The dipole, quadrupole, octupole, hexadecapole moments and the dipole, dipole-quadrupole, dipole-octupole, quadrupole-quadrupole polarizabilities of H₂, O₂, N₂, CO₂, CO, CN, HCl, HCN, NaCl, OH, N₂H⁺, CH₄, H₂O molecules have been calculated using ab initio methods (R)CCSD(T) and CCSD(T) of high level with different aug-ccVXZ bases (X = Q, 5).

The weakly selective (continuum) absorption of electromagnetic radiation by water vapour is an important factor affecting the radiative balance of the Earth’s atmosphere, and is the main component of absorption in the IR atmospheric windows. The possible physical origin of this phenomenon is being discussed for more than 50 years. This paper gives a retrospective analysis and description of the current status in the problem of the water vapour continuum absorption. A brief description of the existing water vapour continuum models is presented including their advantages and shortcomings. The most interesting experimental and theoretical results of the recent years are discussed.

The basic concepts of the spectral line shape theory are outlined, which are essential for understanding the physical pattern of the absorption process at frequencies far from the line centers and characterize the theory as the independent part of spectroscopy. A relatively simple analytical expression for the line shape at large frequency detunings, including parameters of the classical and quantum intermolecular interaction potentials, gives a possibility to describe the spectral and temperature behavior of the absorption in band wings of different gases. It is shown that the general approach to the line shape problem underlying the asymptotical line wing theory enables the opportunity to represent the parameters, which were interpreted till now only from the viewpoint of the dimer hypothesis.

The algebraic approximation of the spectral line profile derived with simultaneous account of small- and large-angle molecular scattering collisions was obtained. Deviations of the approximate line profile from the calculated exact profile do not exceed a tenth of a percent in the range of practically relevant parameters. It was shown that weak collisions with scattering on classical small angles diminish the collision line narrowing, which causes the profile to be flatter than the profile in the strong velocity-changing collisions model. The relative difference of the maximal amplitudes of these profiles can reach 15% that makes the accounting for weak collisions along with strong collisions to be necessary in a quantitative processing of high resolution inhomogeneously broadened spectra.

Information resources on spectroscopy are the most significant part of Institute of Atmospheric Optics SB RAS information resources. Furthermore, information systems Spectra, S&MPO, W@DIS, and HITRAN on the Web, developed via web-technologies, provide for a wide spectrum of researchers with access to verified data, information about this data, and knowledge, which allow processing this information on conceptual level. This article presents a brief description of these information systems. The focus of the work is on the information system W@DIS designed for qualitative analysis of spectroscopic data with different degrees of detailing.

A comparison of atmospheric solar spectra, calculated with different data on the atmospheric gas absorption lines, with the spectra measured by a ground-based Fourier-spectrometer with a high spectral resolution is made. The carbon dioxide and methane total contents in the atmospheric column are retrieved from the measured spectra with the use of modern spectroscopic databases in a direct model. It is shown that the values of the atmospheric methane content retrieved with the use of the recent versions of the HITRAN spectroscopic database differ almost by 2%; for the carbon dioxide, the lesser difference is observed.