The electronic spectrum of the fluoroborane free radical. II. Analysis of laser-induced fluorescence and single vibronic level emission spectra

Abstract

Subsequent to our spectroscopic detection of the HBX (X=F, Cl, Br) free radicals (S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)), the electronic spectrum of the A (2)A(")Pi-X (2)A(') system of the fluoroborane (HBF) radical in the 600-745 nm region has been studied in detail using the pulsed discharge jet technique. The band system involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Pi state at linearity. Using the results of our theoretical study of the ground and excited state vibrational energy levels and (11)B-(10)B isotope shifts (see the companion paper), the vibrational quantum numbers of the bands in the laser-induced fluorescence (LIF) spectra have been assigned. Rotational and vibrational analyses of the LIF and wavelength resolved emission spectra have been carried out, from which the linear excited state and the bent ground state equilibrium configurations have been confirmed. The ground state molecular geometry of HBF has been determined as r(0)(BH)=1.214(2) A, r(0)(BF)=1.303 4(5) A, and theta=120.7(1) degrees. Based on high-level ab initio calculations and symmetry considerations, predissociation of the excited state into H((2)S)+BF((1)Sigma(+)) on the ground state potential energy surface is identified as the cause of the breaking off of fluorescence in the LIF spectra.