3-CHANNEL DIODE-LASER SPECTROMETER FOR THE DETERMINATION OF LINE-SHIFT COEFFICIENTS IN THE NU(3) BAND OF NO2

The implementation of a three channel lead salt diode laser spectromet er and its application for the measurement of line-shift coefficients in the nu(3) band of NO2 are presented. The spectrometer allows the de termination of line shifts larger than 5.10(-4) cm(-1) and is suitable also for the investigation of relatively crowded spectra of molecules like NO? or SO?. For the first time it was possible to determine shif t coefficients for seven lines of the nu(3) band of NO2 in the case of collisions with He, Ne, Ar, Kr, and Xe. Moreover, the spin splitting and the relative intensity of the doublet components were measured for eight unresolved doublets. The shift and broadening coefficients were determined for lines covering the quantum number ranges 24 less than or equal to N '' less than or equal to 38, 1 less than or equal to K-a '' less than or equal to 5, the spin splittings and the intensity rat ios for lines within the intervals 20 less than or equal to N '' less than or equal to 38, 1 less than or equal to K-a '' 5. The broadening data show an excellent agreement with experimental data recently publi shed. The results for the spin splitting correspond to the theoretical expectation, the intensity ratios are in good agreement with experime ntal and theoretical data. These coincidences are prerequisite for the validation of the line-shift data. All shift coefficients measured ar e negative; in the best cases the uncertainties were less than 2%. The absolute values of the line-shift coefficients for the different nobl e gases follow the trend \<\delta(NO2-Ar)\<\delta(NO2-Kr)\<\delta(NO2- Xe)\. Within the studied quantum number range an increase of the absol ute size \delta(NO2-noble gas) with increasing N '' is observed. (C) 1 998 Published by Elsevier Science Ltd. All rights reserved.