High-resolution analysis of the nu(4) absorption band of (CH2BrF)-Br-79

The gas-phase infrared spectrum of the fundamental band of CH 79BrF was recorded in the 1010 –1116 cm1 wavenumber 42 79 region using a TDL spectrometer. In this first high-resolution investigation of the synthesized Br isotopic form, more than 10 200 transitions of this a/b-hybrid band centered at 1068.5385 cm 1 were assigned and, using the Watson’s A-reduced Hamiltonian in the Ir-representation, a reliable set of molecular constants for the excited state v 1 was determined. From 4 ground state combination differences having rotational quantum numbers J and Ka up to 97 and 21, respectively, improved and extended ground state rotational and centrifugal distortion constants were calculated as well. Comparison between the observed and calculated band intensities in appropriate regions of the spectrum gave an estimate of the transition dipole- moment ratio along the a and b axes as a/b 2.0 0.2, in agreement with the predicted theoretical value of 1.99.