The (A)over-tilde (2)Sigma(+) <- (X)over-tilde (2)Pi transition of the NO center dot CH4 and NO center dot CD4 complexes

NO . CH4 and NO . CD4 were studied in a molecular beam, using (1+1) resonan ce-enhanced multiphoton ionization (REMPI) spectroscopy. A detailed spectru m results in each case, with a series of bands observed, assigned to interm olecular vibrations onto which is superimposed further structure. The origi n of this further structure is discussed in the light of previous studies. From the spectrum, a number of intermolecular vibrational frequencies in th e (A) over tilde state were obtained. D-0(') for NO . CH4 (NO . CD4) was me asured as 211 (238) cm(-1); with D-0" for NO . CH4 (NO . CD4) being derived as 117 (122) cm(-1). Ab initio calculations were performed on the (X) over tilde state, and it is deduced that the (X) over tilde state has a C-s glo bal minimum, with the NO pointing towards a CH3 face, with the N tilted tow ards the methane. That said, from the energetic proximity of a number of st ationary points, the complex is expected to be performing wide amplitude mo tion, sampling a wide range of energies even with the zero-point energy.