Details

Autor(en) / Beteiligte

• Kaspar, Johannes
• Smith, Vedene H.
• McMaster, Blair N.

Titel

The stability and specrta of isotopic forms of the ammonium radical: An ab initio CI study of the dissociation barrier

Ist Teil von

• Chemical physics, 1985-06, Vol.96 (1), p.81-95

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

1985

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• The potential barrier for the dissociation of the ammonium radical (NH 4 → NH 3 + H) has been calculated at an ab initio CI level and a vibrational and tunneling-lifetime analysis was made therefrom. In contrast to the UHF results, the zero-point vibrational levels inside the barrier are bound for all isotopic species NH 4, ND 4 and NT 4. For NH 4, one quasibound vibrational level is found while both ND 4 and NT 4 have two quasibound levels. It is suggested that the latter correspond to the “stable” and “dissociative” form of the radical found in neutralized ion beams. Several emission bands are assigned to vibrational transactions of the electronic Rydberg 3p 2T 2-3s 2A 1 transition. It is proposed that the instability of the NH 4 radical, predissociation lifetimes and local NH oscillations are closely related aspects of the radical NH 4 and its isotopic forms. The central feature that connects these aspects is the local character of the vibrations. In contrast to the CH 4 molecule it is more appropriate to think in terms of uncoupled NH bond oscillations than in terms of harmonic normal modes.