Isotope and Quantum Effects in Vibrational State Distributions of Photodesorbed Ammonia

A marked quantum effect has been observed in the vibrational state distribution of photodesorbed ammonia. Namely, for quantum numbers larger than zero, symmetric and antisymmetric levels in the ν2 mode of the desorbed ammonia molecule are unequally populated. A strong propensity for symmetric levels is observed for NH3, whereas the reverse is found for ND3. Model calculations reproduce this effect. Moreover, it is found that the actual ratios probe the binding energy in the energetically less favorable inverted geometry with the H atoms pointing towards the surface