RENNER-TELLER EFFECT ON THE HIGHLY EXCITED BENDING LEVELS OF A (1)A(1) CH2

The effect of Renner-Teller coupling between the ã 1A 1 and b̃ 1B1 states of CH2 on the rotational structure of the ã 1A1 bending vibrational levels has been observed. Renner-Teller coupling causes a decrease in the A rotational constant of the ã 1A1 (0,5,0) level, at 6400 cm-1 above the zero-point level, compared to the value extrapolated from the (0,v2,0) v2=0-4 levels. Excellent agreement is obtained between the experimentally determined A value for (0,5,0) and that predicted by ab initio calculations of Green et al. [J. Chem. Phys. 94, 118 (1991)]. The effect of Renner-Teller coupling on the A rotational constant of bending levels as low as v2=3 has also been detected. The barrier height to linearity in the ã 1A1 state was also estimated by fitting the ã 1A1 bending level term values to a harmonic plus Gaussian perturbation potential function, where the effects of orbital angular momentum were explicitly included to account for electronic-rotational coupling in the calculation. The value of 8600±400 cm-1 obtained is in good agreement with the ab initio result of 8800 cm-1. © 1995 American Institute of Physics.