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

Abstract

Rotational and vibrational temperatures of electronically excited BiN radicals in a low-pressure Bi x +N/N 2*/N 2+Ar chemiluminescent flame have been deduced from high-resolution Fourier-transform emission spectra. Bands of three electronic transitions, a 3Σ +(a 11)→X 1Σ +(X0 +), b 5Σ +(b 10 +)→X 1Σ +(X0 +), and b 5Σ +(b 10 +)→a 3Σ +(a 11), were analysed to determine the optical temperatures in the a 3Σ +(a 11) and b 5Σ +(b 10 +) states. The rotational temperatures characterising the rotational populations in the a 11, v=0 and 1 states were determined from the a 1→X, 0–2, 0–3, 0–4, 1–1, and 1–2 bands. The b 1→X, 0–8 and 0–11 bands, and the b 1→a 1, 0–0 bands served to determine the rotational temperature of the radicals in the b 10 +, 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 a 11 and b 10 + states were derived from band intensities of the a 1→X and from the b 1→X as well as b 1→a 1 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 a 11 vibrational temperature (336±21 K) was close to the rotational temperature, while the b 10 + vibrational temperature (438±36 K) differed, likely due to the previously observed perturbation of the b 10 + state.