Isotope and Quantum Effects in Vibrational State Distributions of Photodesorbed Ammonia

Abstract

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 n 2 mode of the desorbed ammonia molecule are unequally populated. A strong propensity for symmetric levels is observed for NH 3 , whereas the reverse is found for ND 3 . 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. [S0031-9007(97)

Vibrationally enhanced associative photodesorption of molecular hydrogen from Ru(0001)

“…From experience with similar systems [6][7][8][45][46][47], however, it is expected to be in the few-fs regime, and will therefore be chosen below from this range as an empirical parameter. Vibrational relaxation on a timescale s vib will be neglected as far as DIET is concerned, since the desorption process is very fast.…”

Dissociation of a Surface Bond by Direct Optical Excitation: H-Si(100)

“…Nearly all photodesorption studies point to indirect mechanisms, e.g., those due to hot substrate carriers [1][2][3] or to the transfer of intramolecular excitation to the desorption coordinate. The best example for the latter is the vibrationally mediated UV photodesorption mechanism for ammonia from semiconductor and metal surfaces, as discovered by Zhu and White [7] and explored by a number of other groups [8][9][10][11]. Rotational motion in an adsorbed molecule may also strongly couple to the desorption process, e.g., in hot electron mediated photodesorption NO from NiO [12] and in electron stimulated desorption of NO from Pt [13].…”

Quantum dynamics of laser- and field-induced desorption of molecules from metal surfaces

“…This field-induced desorption has been achieved already for large, highly polarizable molecules such as DNA bases on insulator surfaces [23]. This question shall be here answered for the NH 3 /Cu(111) system, for which also laserinduced DIET has been reported [24,25] and studied theoretically [26 -28].…”

“…For that purpose a model involving at least two modes (the molecule-surface distance Z and the "inversion" or "umbrella" mode of ammonia, x) proved to be essential to explain experimental facts such as large isotope effects in the total [24] and state-resolved [25] desorption yields. In this article, however, this reaction mechanism is of little concern, while another possible desorption scenario which proceeds solely in the ground electronic state will be suggested, namely desorption by strong static or slowly varying electric fields.…”

“…As mentioned above, substrate-mediated laser desorption of neutral molecules has also been realized for the ammonia/copper system [24,25]. An open-system density matrix model was used which successfully accounted for major experimental observations [27].…”