Hamburg 2009 – scientific programme

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MO: Fachverband Molekülphysik

MO 20: Photochemie 1

MO 20.4: Talk

Thursday, March 5, 2009, 11:45–12:00, VMP 6 HS-G

Photodissociation dynamics of trans-methyl nitrite studied by velocity map imaging — •Siarhei Dziarzhytski and Friedrich Temps — Institut für Physikalische Chemie Christian-Albrechts-Universität zu Kiel Olshausenstr. 40, D-24098 Kiel

The dissociation dynamics of methyl nitrite (CH₃ONO) provides an interesting test for the theory of photodissociation. The knowledge about the NO and CH₃O internal energy distributions and their dependences on the initial vibrational state provides insight into the dissociation dynamics and the potential energy surface of the excited electronic state. The task is to establish the correct pathway for photodissociation, the determination of which strongly depends on the correct assignment of the UV absorption spectrum of methyl nitrite. The photolysis of trans-methyl nitrite excited to the S₁ state with 0 and 1 quanta of excitation in the N=O - stretching mode has been investigated. The primary NO fragments were probed by (1+1) REMPI in specific rovibrational states. Two dissociation pathways were found: a vibrationally non-adiabatic predissociation, and an adiabatic channel via tunneling through a potential barrier on the S₁ potential energy surface. The O-NO bond dissociation energy was determined to be D₀ = 13 560 ± 200 cm⁻¹ and an S₁ excited state lifetime of τ ≈ 350 fs was found. The data support previous experimental and theoretical results on cis-methyl nitrite and unambiguously settle the question of the correct vibrational band assignment in the UV spectrum of cis-isomer.