Nessler, Winfried; Bornscheuer, Karl-Heinz; Hertel, Tobias; Hasselbrink, Eckart:

Internal Quantum State Distributions of NH₃ Photodesorbed from Cu(111) at 6.4 eV.

In: Chemical Physics (Chem.Phys.), Jg. 205 (1996) ; Nr. 1,2, pp. 205-219
ISSN: 0301-0104
Zeitschriftenaufsatz / Fach: Chemie
The UV photodesorption (6.4 eV) of NH₃ from Cu (111) was studied by using resonance enhanced multiphoton ionization through the .hivin.B <- .hivin.X transition for state specific detection. The authors measured the relative populations of both inversion doublet states of the 1st 3 vibrational levels in the ν₂ mode and the rotational excitation of photodesorbed NH₃. The av. energy content in the ν₂ mode corresponds to a temp. of Tν₂ = 1000 K which is significantly larger than the translational energy released normal to the surface {Etrans}/2k = 600 K. A marked underpopulation of the antisym. ν₂ levels was obsd. The rotations can be described by a Boltzmann distribution with a temp. close to the surface temp. indicating that the mols. do not experience significant torque during the desorption process. No pronounced correlation effects in the population of different degrees of freedom are found. These exptl. results are consistent with the assumption that the energy required for desorption is transferred from the initial electronic excitation to the mol.-surface bond via the intramol. coordinate ν₂.