Elsevier

Chemical Physics

Volume 93, Issue 2, 15 February 1985, Pages 293-306
Chemical Physics

Predissociation dynamics of Ã-state ammonia probed by two-photon excitation spectroscopy

https://doi.org/10.1016/0301-0104(85)80026-4Get rights and content

Abstract

Electronically excited ND3(A¯) molecules have been prepared by laser two-photon excitation on theA¯1A″2—X¯11 transition and monitored via their resulting short-lived emission. The earlier observation of Douglas that ND3(A¯) molecules carrying one quantum of out-of-plane bending vibration ν′2 are least susceptible to predissociation, is confirmed. ND3(A¯) predissociation rates are found to be both vibronic and rovibronic level dependent. Both observations may be understood by considering the likely form of the potential energy surface for ND3(A¯) molecules in the region of the D2N—D dissociation coordinate. At short D2N—D separations this surface exhibits a barrier. The presence of a conical intersection (involving the ND3 ground state surface) further out along the dissociation coordinate has a crucial influence on the magnitude of this barrier. The envisaged form of theA¯-state potential energy surface also provides a qualitative rationale for all previous experimental findings concerning electronic branching ratios and energy disposal amongst the primary photofragments arising in the photodissociation ofA¯-state ammonia.

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