Rotational and vibrational temperatures of electronically excited BiN radicals in a chemiluminescent flame

Rotational and vibrational temperatures of electronically excited BiN radicals in a low-pressure Bix+N/N2*/N2+Ar chemiluminescent flame have been deduced from high-resolution Fourier-transform emission spectra. Bands of three electronic transitions, a3Σ+(a11)→X1Σ+(X0+), b5Σ+(b10+)→X1Σ+(X0+), and b5Σ+(b10+)→a 3Σ+(a11), were analysed to determine the optical temperatures in the a3Σ+(a11) and b5Σ+(b10+) states. The rotational temperatures characterising the rotational populations in the a11, v=0 and 1 states were determined from the a1→X, 0-2, 0-3, 0-4, 1-1, and 1-2 bands. The b1→X, 0-8 and 0-11 bands, and the b1→a1, 0-0 bands served to determine the rotational temperature of the radicals in the b10+, v=0 state. The temperatures derived from the various bands and transitions were well consistent and the mean rotational temperature was determined to be 353±18 K, which is close to the translational temperature of the gas.Vibrational temperatures of the radicals in the a11 and b10+ states were derived from band intensities of the a1→X and from the b1→X as well as b1→a1 systems, respectively. The Franck-Condon factors needed were calculated with RKR potentials deduced from literature values of the rotational and vibrational constants in the three states involved. The a11 vibrational temperature (336±21 K) was close to the rotational temperature, while the b10+ vibrational temperature (438±36 K) differed, likely due to the previously observed perturbation of the b10+ state.