EXCITED-STATES AND PHOTOCHEMISTRY OF SATURATED MOLECULES .7. POTENTIAL-ENERGY SURFACES IN EXCITED SINGLET-STATES OF METHANE

Potential energy surfaces are investigated for a number of low-lying excited singlet states of methane, using a split valence plus Rydberg basis set and singly excited CI. Of the six minima found, the lowest two are valence states. The lowest minimum corresponds to the products 11B 1CH2 + 11Σg+H 2, in agreement with the observed threshold photochemistry, and is accessible by five separate routes from the lowest vertical state. The second valence minimum is a square planar structure. Of the four Rydberg minima detected, one is a local minimum on the otherwise dissociative B1 surface and two correspond closely to CH4+ structures previously determined. None of the minima have a structure from which the radical products CH3. + H- are likely to be obtained. © 1979 American Institute of Physics.