THE X21-]X10+ ELECTRONIC BAND SYSTEMS OF BISMUTH MONOHALIDES IN THE NEAR-INFRARED

Emission spectra of the transitions X21-->X10+ between the fine-structure components of the X 3-SIGMA- ground states of BiF, BiCl, BiBr and BiI have been observed in the near-infrared spectral region between 1.3 and 1.7-mu-m. The X(2)1 states of the radicals were excited by near-resonant electronic-to-electronic (E-E) energy exchange from metastable O2 (a 1-DELTA-g) molecules in a fast-flow system. For each molecule, a number of blue-degraded bands with sharp heads in the P branches were measured in the DELTA-upsilon = 0, +/- 1 and -2 sequences at spectral resolutions between 0.1 and 1 cm-1 using a Bomem Fourier-transform spectrometer. The following electronic term values and vibrational constants of the X21 states were obtained (in cm-1): T(e) = 6752.7944(12), 6670.83(15), 6526.44(24), 6181.64(6), omega-e = 543.0558(24), 327.44(15), 220.38(21), 168.68(6), omega-e-chi-e = 2.3996(15), 1.004(27), 0.546(36), 0.386(6), for BiF, Bi Cl-35, Bi Br-79 and BiI, respectively, where the error limits are 3-sigma. From a re-interpretation of near-UV spectra of BiF, the a2(a 1-DELTA) state of BiF is calculated to lie at 11555 cm-1.