Absorption spectroscopy of singlet CH2 near 9500 cm(-1)

The (b) over tilde B-1(1)-(a) over tilde (1)A(1) spectrum of methylene betw een 9317 and 9610 cm(-1) was recorded using frequency-modulated diode laser absorption spectroscopy. This is the lowest-energy region ever observed in the CH2((b) over tilde B-1(1)) electronic state. Transitions to four upper rovibronic levels were identified using known ground-state combination dif ferences. On the basis of comparison with published results of ab initio ca lculations, they were assigned to levels with both (a) over tilde and (b) o ver tilde primary electronic wave function character: K = 0 (b) over tilde (0,1,0), K = 4 (b) over tilde (0,0,0), K = 1 (a) over tilde (0,8,0), and K = 0 (b) over tilde (0,2,0). The first three of these levels had not previou sly been observed. The rotational assignments of the last, K = 0 (b) over t ilde (0,2,0), observed via transitions from the (a) over tilde (0,1,0) vibr ationally hot bending level, differ from the original assignments of Herzbe rg and Johns [Proc. R. Sec. London, Ser. A 1966, 295, 107]. A comparison wi th the results of the most recent high-level quantum chemical calculations suggests that further refinement of the potential energy surface of the b s tate near its equilibrium would be desirable.