L. Regalia

Multispectrum fitting technique for data recorded by Fourier transform spectrometer: application to N2O and CH3D

Abstract To improve the fit of spectroscopic parameters recorded by Fourier transform spectrometer (intensities, broadening coefficients, and pressure shift), we have developed a multispectrum fitting technique, this technique being already described by other research groups (Benner DC, Rinsland CP, Malathy Devi V, Smith MAH, Atkins D. JQSRT 1995;53:705; Carlotti, Appl Opt 1988;27:3250). We describe the algorithm of the software allowing to analyse and visualise several spectra simultaneously. To validate our software, line intensities (for N 2 O and CH 3 D) and self-broadening coefficients were fitted and compared with previous studies. We have also studied the wave numbers of N 2 O and compared them with heterodyne measurements in order to estimate the relative accuracy of our results.

Broadening parameters of NO2 lines in the 3.4 μm spectral region

Abstract Fourier transform spectra have been recorded to measure self-, N 2 -, and O 2 -broadening coefficients of NO 2 lines in the v 1 + v 3 band. For the studied set of transitions, a slight rotational dependence of the broadening coefficients exists versus N ″, the rotational quantum number of the lower level of the transition, whereas no significant dependence is observed versus K a ″. An empirical relation, allowing one to calculate approximate values of the air-broadening coefficients γ air 0 , at 296 K, for lines observable in atmospheric spectra recorded from the ground, is proposed: γ air 0 = 84.1 − 0.753 N ″ + 0.0059 N ″ 2 , in 10 −3 cm −1 ·atm −1 , with an uncertainty of about ± 10% when N ″ and K a ″ are smaller than about 40 and 10, respectively. For typical lines used for atmospheric applications, the single value reported in the HITRAN database for all lines of all bands of NO 2 can differ by more than 20% from the measured ones.

Intensities of N2O measurements in the 4 and 3 μm region using fourier transform spectrometer

Abstract Absolute intensities of transitions of four bands of N 2 O in very good self consistency are obtained and compared with recent literature data. Intensities from the transition dipole moment are also calculated. To obtain these results, special care is taken for all experimental set-up and to obtain a true zero transmittance for the Fourier Transform Spectrometer of Reims, working in stepping mode. Three types of improvements are performed leading to a zero level better than 0.5% and then resulting in an absolute accuracy better than 2% in the intensity measurements for N 2 O.

Variation of the experimental conditions during the recording in FTS: Effects on the determination of line intensities and collisional widths

Abstract The errors which affect measured line intensities and collisional widths, because of the variation of the experimental conditions during the recording in FTS laboratory experiments, are studied. For step-by-step as well as for rapid scan interferometers, quasi-Doppler, Voigt, and quasi-Lorentzian line profiles are considered. As examples, the cases of adsorption and desorption, of decomposition of the absorbing gas, and of weak variation of the temperature, are discussed in detail.