The accurate determination of spectroscopic constants for a dark vibrational state: The Coriolis coupled ν4 and ν6 bands of D11BF2

Abstract

The high resolution infrared spectrum of deuterated difluoroborane, DBF2, has been recorded from 700 to 912 cm−1. At low resolution, the only observable bands in this region belong to the c-type, out-of-plane deuterium motion, ν4, of the two B isotopomers. Upon analysis of the ν4 fundamental in D11BF2, a large perturbation was observed due to a ΔK=±1 Coriolis interaction with a dark vibrational state. The dark state was presumed to be the unseen, a-type, in-plane D–B rocking fundamental, ν6. A novel method of upper state energy level interlacing was used to determine A, B+C and T0 for the dark excited state, 61, the band origin, rotational and centrifugal distortion constants for the 41 state, and ξ4,6b (≊2ζ4,6bB). Based upon these constants, ν6 transitions were predicted and located in the region of the perturbation. Experimentally determined Coriolis, rotational, and centrifugal distortion constants are reported. The experimental results are compared with the results from ab initio calculations.