High resolution analysis of the complex symmetric CF_3 stretching chromophore absorption in CF_3I

摘要

We report a detailed high resolution rovibrational analysis of the v_1 fundamental absorption band system of CF_3I, which appears as a very complex resonance polyad. Pulsed slit jet diode laser spectra (instrumental bandwidth <=25 MHz) of CF_3I (neat and seeded in He) at rotational temperatures of about 7, 30, and 70 K have been obtained. The low J, K part of the observed transitions cna be fitted by a model including the anharmonically coupled levels v_1(v_0 = 1076.0551 cm~(-1)), 2v_5~0(v_0=1079.6732 cm~(-1)) and v_3+3v_6~(+-3)(v_0=1072.3884 cm~(-1)), and the local Coriolis perturber v_3+3v_6~(+1)(v_0=1074.1845 cm~(-1)). The level v_3+3v_6~(+3) was observed and included for the first time, and an additional anharmonic coupling between the levels v_3+3v_6~(+3) and v_3+3v_6~(-3) proved relevant. In order to analyze the higher J,K regions, perturbations arising from 2v_5~(+-2) turned out to be importnat. In certain regions of the spectra, effect due to nuclear quadrupole interaction are clearly visible. We report new sets of parameters for a low J, K model and for an extended model including the perturber 2v_5~(+-2). The results are discussed in relation to infrared multiphoton excitation of CF_3I, infrared absorption in the atmospheric window and intramolecular vibrational redistribution.