Lambda. -doublet substate specific investigation of rotational and fine structure transitions in collisions of OH with H sub 2 and D sub 2

Journal Article · Tue Oct 15 00:00:00 EDT 1991 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.461598· OSTI ID:5220711

Andresen, P; Aristov, N; Beushausen, V; Haeusler, D; Luelf, H W ^[1]

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1. Max-Planck-Institut fuer Stroemungsforschung, 34 Goettingen (Germany)

The selective population of rotational, spin, and {Lambda}-doublet states of OH({sup 2}{Pi},{ital v}=0,1) by inelastic collisions with H{sub 2} and D{sub 2} is investigated in two experiments. In the first experiment OH radicals are generated by photolysis inside a pulsed nozzle beam source and prepared in the ground state {ital j}=1.5, {ital v}=0, {sup 2}{Pi}{sub 3/2} with equal amounts in both {Lambda}-doublets by rotational cooling in the subsequent expansion. The collisional excitation of OH by the secondary beam is probed via laser-induced fluorescence selectively for the {Lambda}-doublet states for the different rotational levels in both spin manifolds of {ital v}=0. Integral cross sections {sigma}({ital j}=1.5,{bar {Omega}}=1.5{r arrow}{ital j} {prime},{bar {Omega}}{prime},{epsilon}{prime}) averaged over the {Lambda}-doublet substates in the input channel, but {Lambda}-doublet substate resolved in the output channel are obtained in this case. In contrast to some previous predictions the {Pi}({ital A}{prime}) {Lambda}-doublet substate is preferentially populated. This implies a population inversion in the {Lambda}-doublets for {sup 2}{Pi}{sub 1/2} and an anti-inversion for {sup 2}{Pi}{sub 3/2}, which rules out previously proposed pump mechanisms for astronomical OH masers. In the second experiment OH is generated also by photolysis, in this case however in a flow system. Single {Lambda}-doublet states are prepared by infrared excitation of the thermally relaxed OH in {sup 2}{Pi}{sub 3/2}, {ital v}=1 for two rotational states ({ital j}=1.5,4.5). The redistribution in {ital v}=1 induced by collisions with H{sub 2} is probed by laser-induced fluorescence. Rate constants are obtained for transitions from the initially prepared {Lambda}-doublet states to the other {Lambda}-doublet of the same {ital j} and also for transitions to other rotational states.

• OSTI ID: 5220711
• Journal Information: Journal of Chemical Physics; (United States), Vol. 95:8; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
DEUTERIUM
MOLECULE-MOLECULE COLLISIONS
HYDROGEN
HYDROXIDES
ROTATIONAL STATES
FINE STRUCTURE
FLUORESCENCE
GROUND STATES
INELASTIC SCATTERING
LASER SPECTROSCOPY
NOZZLES
PHOTOLYSIS
PULSES
RADICALS
CHEMICAL REACTIONS
COLLISIONS
DECOMPOSITION
ELEMENTS
ENERGY LEVELS
EXCITED STATES
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPES
LIGHT NUCLEI
LUMINESCENCE
MOLECULE COLLISIONS
NONMETALS
NUCLEI
ODD-ODD NUCLEI
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
SCATTERING
SPECTROSCOPY
STABLE ISOTOPES
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena