Collisional vibrational relaxation of a triplet state: Energy-dependent energy loss from [ital T][sub 1] pyrazine

Journal Article · Thu Apr 15 04:00:00 EDT 1993 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.464825· OSTI ID:5406656

Bevilacqua, T J; Weisman, R B ^[1]

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1. Department of Chemistry and Rice Quantum Institute, Rice University, Houston, Texas 77251 (United States)

The loss of vibrational energy from gas phase [ital T][sub 1] pyrazine molecules has been measured for thermal collisions with helium, argon, H[sub 2], SF[sub 6], and ground state pyrazine. Triplet pyrazine was prepared with a well defined vibrational energy of 5433 cm[sup [minus]1] through [ital S][sub 1][r arrow][ital T][sub 1] intersystem crossing following optical excitation to the 8[ital a][sup 1] level of [ital S][sub 1]. The time-dependent vibrational energy content of the excited pyrazine molecules was then deduced using a recently developed direct'' method involving the kinetics of subsequent [ital T][sub 1][r arrow][ital S][sub 0] intersystem crossing. For each of the collision partners studied, it was possible to find the average energy lost per gas kinetic collision for donor energies ranging from ca. 2000 to 5433 cm[sup [minus]1]. The magnitudes of these energy losses generally increased with the mass and vibrational complexity of the relaxing collision partner. For vibrational energy contents near 5000 cm[sup [minus]1], relaxation of the triplet pyrazine was enhanced by factors of as much as 24 relative to [ital S][sub 0] benzene at a similar vibrational energy. In addition, with all collision partners studied the average energy lost per collision showed appparent threshold behavior near 3000 cm[sup [minus]1], increasing by approximately an order of magnitude as the donor's energy increased from 2500 to 5000 cm[sup [minus]1]. The findings of this first quantitative study of triplet relaxation suggest that collisional vibrational energy transfer from organic triplet states may proceed by mechanisms different from those that dominate ground state relaxation.

• OSTI ID: 5406656
• Journal Information: Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 98:8; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

664300* -- Atomic & Molecular Physics-- Collision Phenomena-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ARGON
ATOM COLLISIONS
ATOM-MOLECULE COLLISIONS
AZINES
COLLISIONS
ELASTIC SCATTERING
ELEMENTS
ENERGY LEVELS
ENERGY LOSSES
ENERGY TRANSFER
EXCITED STATES
FLUIDS
FLUORIDES
FLUORINE COMPOUNDS
GASES
GROUND STATES
HALIDES
HALOGEN COMPOUNDS
HELIUM
HETEROCYCLIC COMPOUNDS
HYDROGEN
LOSSES
MOLECULE COLLISIONS
MOLECULE-MOLECULE COLLISIONS
MULTIPLETS
NONMETALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRAZINES
RARE GASES
RELAXATION
SCATTERING
SULFUR COMPOUNDS
SULFUR FLUORIDES
TIME DEPENDENCE
TRIPLETS
VIBRATIONAL STATES