Predissociation of CH B2Σ+ v′=0,1 levels studied by cavity ring-down absorption spectroscopy

Cavity ring-down (CRD) absorption spectroscopy is applied to study predissociation of the CH B2Σ+ v′=0, N′=17–19 and v′=1, N′=9–11 rotational levels in a low pressure methane/air flame. Collision-free lifetimes from broadened spectral lineshapes are 45±6 and 10.0±1.5 ps for CH B2Σ+ v′=0, N′=18, 19 and 75±15, 15±2 and 5±1 ps for CH B2Σ+ v′=1, N′=9–11. These lifetimes are in good agreement with previous calculations by Wyel theory using potentials calculated by the iterative Rydberg–Klein–Dunham method [N. Elander, et al., Phys. Scr. 20 (1979) 631]. Experimental results suggest that the F2 spin–orbit levels might predissociate slightly faster than F1 levels.