RESUMEN
Spectra of the symmetric nu1 vibration of the NO dimer have been recorded in gas phase at low temperature, with a high-resolution infrared Fourier transform spectrometer. All the lines were least-squares fitted to a Voigt profile convoluted with the well-known apparatus function of the spectrometer. By means of this method, the frequencies of more than 109 new lines were measured. From the intensities of a set of 33 well-fitted and completely isolated lines, the transition moment was extracted. NO-broadening coefficients of the dimer lines were also measured as well as the predissociation time, which was found to be (2.65 +/- 0.53) ns. Copyright 1999 Academic Press.
RESUMEN
The symmetric nu1 and antisymmetric nu5 vibrations of (NO)2 have been recorded at very low rotational temperature (4 K) using a molecular jet coupled with a high-resolution Fourier transform spectrometer (Bruker IFS 120 HR). A White-type multipass setup allowed us to record the very weak absorption of this dimer. A vibrational predissociation time equal to 75 ps was measured for the nu5 band, in good agreement with values directly derived from photodissociation measurements. This result shows that previous data obtained from spectra recorded using a low-temperature cell at thermodynamical equilibrium were distorted under the effect of molecular collisions. Copyright 1998 Academic Press.
RESUMEN
Fourier spectra of methyl chloride have been obtained at ambient laboratory temperature under self-broadening conditions. Five thousand two hundred and sixty rovibrational transitions of the (nu2, nu5, 2nu3)-vibrational-band triad have been assigned, and new ground and excited state rotational constants for CH335Cl and CH327Cl have been determined. The nu5 and nu2 vibrational-band intensities are determined to be, respectively, 42(1.2) and 31.7(0.9) cm-2 atm-1. Self-broadening coefficients of individual rovibrational lines are determined for the nu5 band of CH335Cl and CH337Cl at 296 K. The self-broadening coefficients peak broadly close to the maximum in the Boltzmann rotational population; no specific trends of the broadening coefficients are observed with the rotational quantum number K. With the exception of the RQ(J, 0) branch, the 1260-1650 cm-1 spectral region can be well modeled by the superposition of overlapping Voigt line profiles. To adequately model the densely packed RQ(J, 0) branch, however, we included collisional line mixing with A+ to A- in addition to A- to A- and A+ to A+ |DeltaJ| >/= 1, DeltaK = 0 collisional transitions allowed. Copyright 1998 Academic Press.
RESUMEN
The broadening of CO(2) rotation-vibration lines has been investigated in the 200-300 K temperature range. From an analysis of four lines (|m| = 8, 15, 20, 30), it is found that the temperature exponent is nearly independent of the rotational quantum number within the limits of experimental error, for both self- and oxygen broadening. Average values n(1) = 0.86 for CO(2)-CO(2) and n(2) = 0.94 for C0(2)-0(2) have been obtained. Comparison is made with the results of the theoretical calculation based on the Robert-Bonamy model.
RESUMEN
The high-resolution FT interferometer of the Laboratoire d'Infrarouge at Orsay has been used to investigate the broadening of N(2)O lines in the 4- and 8-microm spectral regions. All data were taken at both room temperature and 220 K. The uncertainty of the measured values of linewidths was estimated to <4%. From these data, the exponent n of the temperature dependence of linewidths was experimentally determined for the first time, for the systems N(2)O-N(2)O, N(2)O-N(2), and N(2)O-O(2). In the first two cases, it was shown that n is nearly J-independent, whereas it seems to vary linearly for N(2)O-O(2). Finally the values of N(2)O air-broadened linewidths were derived for the two temperatures 295 K and 220 K representing the upper and lower boundaries of middle atmosphere temperatures.
RESUMEN
The considerable increase in high-resolution Fourier transform spectra has led to a practical method of deriving individual line parameters from Fourier data. This method concerns in the main those spectra exhibiting moderately dense structure, so that spectral analysis can be carried out in pressure conditions where collisional broadening dominates: (1) For any line under study, the strength and width values can be determined simultaneously from the same spectrum. (2) Instrumental distortions can be reduced by pressurizing the gas sufficiently. In the present case the relevant corrections do not exceed 3%, in a few cases 5%. (3) Thus, from the analytical expression of the apodized apparatus function, it is possible by means of a convolution calculation to draw up a series of tabulations. These give the true linewidth and the dimensionless quantity K(sigma(0))l, respectively, as functions of the width and maximum transmission of the observed contour. The calculation has been extended to the case of doublets of the same intensities, widths, and known spacing. The method has been tested by investigating a few self-broadened lines in the 12 degrees 0-00 degrees 0 transition of N(2)O and some nitrogen-broadened lines in the fundamental band of NO recorded at the laboratory by G. Guelachvili.
