High resolution analysis of the complex symmetric CF3 stretching chromophore absorption in CF3I

Abstract

We report a detailed high resolution rovibrational analysis of the ν 1 fundamental absorption band system of CF 3 I , which appears as a very complex resonance polyad. Pulsed slit jet diode laserspectra (instrumental bandwidth ⩽25 MHz) of CF 3 I (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 can be fitted by a model including the anharmonically coupled levels ν 1 (ν̃ 0 =1076.0551 cm −1 ), 2ν 5 0 (ν̃ 0 =1079.6732 cm −1 ) and ν 3 +3ν 6 ±3 (ν̃ 0 =1072.3884 cm −1 ), and the local Coriolis perturber ν 3 +3ν 6 +1 (ν̃ 0 =1074.1845 cm −1 ). The level ν 3 +3ν 6 +3 was observed and included for the first time, and an additional anharmonic coupling between the levels ν 3 +3ν 6 +3 and ν 3 +3ν 6 −3 proved relevant. In order to analyze the higher J, K regions, perturbations arising from 2ν 5 ±2 turned out to be important. In certain regions of the spectra, effects due to nuclear quadrupoleinteraction are clearly visible. We report new sets of parameters for a low J, K model and for an extended model including the perturber 2ν 5 ±2 . The results are discussed in relation to infrared multiphoton excitation of CF 3 I , infrared absorption in the atmospheric window and intramolecular vibrational redistribution.