Alexander D. Bykov

CDSD-1000, the high-temperature carbon dioxide spectroscopic databank

Abstract We present a high-temperature version, CDSD-1000, of the carbon dioxide spectroscopic databank. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths and coefficients of temperature dependence of air-broadened half-widths) of the four most abundant isotopic species of the carbon dioxide molecule. The reference temperature is T ref =1000 K and the intensity cutoff is I cut =10 −27 cm −1 / molecule cm −2 . More than 3 million lines covering the 260–8310, 418–2454, 394–4662, and 429– 2846 cm −1 spectral ranges for 12 C 16 O 2 , 13 C 16 O 2 , 12 C 16 O 18 O , and 12 C 16 O 17 O , respectively, are included in CDSD-1000. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. Line-by-line simulations of several low- and medium-resolution high-temperature (T=800– 3000 K ) spectra have been performed in order to validate the databank. Comparisons of CDSD-1000 with other high-temperature databanks HITEMP, HITELOR, and EM2C are also given. CDSD-1000 is able to reproduce observed spectra in a more satisfactory way than the high-resolution databank HITEMP for temperatures higher than 1000 K . The databank is useful for studying high-temperature radiative properties of CO2. CDSD-1000 is freely accessible via the Internet.

The High-Resolution Spectrum of Water Vapor between 11 600 and 12 750 cm-1

The absorption spectrum of water vapor has been recorded between 11 600 and 12 750 cm-1 with a Fourier transform spectrometer (Kitt Peak, Az) at a resolution of 0.012 cm-1 and with a path length of 434 m. The line assignment has led to the determination of 506 accurate energy levels of the (310) (211), (112), (013), (230), (131), (032), and (051) vibrational states which belong to the so-called 3nu + delta resonance polyad. The rotational energy levels obtained are on the average in agreement with those reported recently by R. Toth (J. Mol. Spectrosc. 166, 176-183 (1994)) for the strong bands, but there are differences for high J levels or weak bands levels (about 15% of all levels). The experimental rotational energy levels have been fitted using Pade-Borel approximants and a set of 104 vibrational energies and rotational, resonance, and centrifugal distortion constants for the (310), (211), (112), (013), (230), (131), (032), and (051) vibrational states have been determined.

Semi-empiric approach to the calculation of H2O and CO2 line broadening and shifting

Abstract A semi-empiric approach to the calculation of spectral line half-widths and shifts is proposed. This approach is based on the Anderson approximation and includes the correction factors, the parameters of which can be determined by fitting the broadening or shifting coefficients to the experimental data. This allows sufficiently accurate predictions of the parameters of line profiles that were not measured. The coefficients of CO2 and H2O spectral line broadening and shifting due to air and nitrogen pressure are calculated, as well as the coefficients of their temperature dependence. The calculated coefficients agree satisfactorily with measured values.

An expert system for identification of lines in vibrational-rotational spectra

An expert system for automatic identification of the complex vibrational-rotational spectra of molecules has been developed. An iteration approach is implemented in this system, in which employment of the exact combination rule is combined with determination of the spectroscopic constants by solving of the inverse problems and comparison of the calculated parameters of spectral lines with the corresponding measured values. In order to calculate the energy levels and the frequencies and intensities of lines, the Watson Hamiltonian, the Padé-Borel approximants, and generating functions are used. The system is based on the application of pattern-recognition algorithms. Recognition training makes it possible to obtain the required flexibility of the system and to use different methods of identification based on the application of combination rules both for the analysis of strong bands and for the assignment of weak single lines. The system developed can be used to analyze the spectra of the Cs and C2V molecules, as well as employ the calculated spectrum of a molecule of any type prepared in advance. This system was successfully used to identify the H216O, H217O, H218O, D2O, HDO, H232S, H234S, and H233S and molecules.

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.

J-dependence of the lineshift coefficients in the ν2 water vapor band

Abstract The nitrogen pressure shifting coefficients for the 150 water vapor lines in the ν 2 band have been measured with the Fourier transform spectrometer located at the Paris VI University with the spectral resolution of 0.005 cm −1 and at room temperature. The measurements were performed for lines having lower state angular moment up to 16, the measured values are found to range from + 0.015 to −0.0293 cm −1 /atm. The J -dependence of the line shift coefficients was studied using the Anderson-Tsao-Curnutte model and cut-of-free method. Fairly satisfactory agreement between measured and calculated line shift coefficients has been found.

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.

Application of pattern recognition in molecular spectroscopy: Automatic line search in high-resolution spectra

An expert system has been developed for the initial analysis of a recorded spectrum, namely, for the line search and the determination of line positions and intensities. The expert system is based on pattern recognition algorithms. Object recognition learning allows the system to achieve the needed flexibility and automatically detect groups of overlapping lines, whose profiles should be fit together. Gauss, Lorentz, and Voigt profiles are used as model profiles to which spectral lines are fit. The expert system was applied to processing of the Fourier transform spectrum of the D2O molecule in the region 3200–4200 cm−1, and it detected 4670 lines in the spectrum, which consisted of 439000 dots. No one experimentally observed line exceeding the noise level was missed.

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.

Absorption spectra of deuterated water vapor

The HDO and D2O spectra have been recorded at room temperature with a high resolution Fourier-Transform spectrometer and a multipass cell with an absorption path length of 240 meters. The resolution used was about 0.01 cm-1, the relative uncertainty in line positions was approximately +/- 0.0002 cm-1.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.