Details

Autor(en) / Beteiligte

• Muskatel, B. H.
• Remacle, F.
• Thiemens, Mark H.
• Levine, R. D.

Titel

On the strong and selective isotope effect in the UV excitation of N₂ with implications toward the nebula and Martian atmosphere

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2011-04, Vol.108 (15), p.6020-6025

Ort / Verlag

United States: National Academy of Sciences

Erscheinungsjahr

2011

Quelle

MEDLINE

Beschreibungen/Notizen

• Isotopic effects associated with molecular absorption are discussed with reference to natural phenomena including early solar system processes. Titan and terrestrial atmospheric chemistry, and Martian atmospheric evolution. Quantification of the physicochemical aspects of the excitation and dissociation processes may lead to enhanced understanding of these environments. Here we examine a physical basis for an additional isotope effect during photolysis of molecular nitrogen due to the coupling of valence and Rydberg excited states. The origin of this isotope effect is shown to be the coupling of diabatic electronic states of different bonding nature that occurs after the excitation of these states. This coupling is characteristic of energy regimes where two or more excited states are nearly crossing or osculating. A signature of the resultant isotope effect is a window of rapid variation in the otherwise smooth distribution of oscillator strengths vs. frequency. The reference for the discussion is the numerical solution of the time dependent Schrödinger equation for both the electronic and nuclear modes with the light field included as part of the Hamirtonian. Pumping is to all extreme UV dipole-allowed, valence and Rydberg, excited states of N₂. The computed absorption spectra are convoluted with the solar spectrum to demonstrate the importance of including this isotope effect in planetary, interstellar molecular cloud, and nebular photochemical models. It is suggested that accidental resonance with strong discrete lines in the solar spectrum such as the Clll line at 97.703 nm can also have a marked effect.