Reaction dynamics of metastable helium molecules and atoms near 4. 2 K

Journal Article · Thu Jul 01 04:00:00 EDT 1993 · Physical Review A; (United States)

DOI:https://doi.org/10.1103/PhysRevA.48.364· OSTI ID:6381616

Tokaryk, D W; Brooks, R L; Hunt, J L ^[1]

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1. Guelph-Waterloo Program for Graduate Work in Physics, University of Guelph, Guelph, Ontario, N1G2W1 (Canada)

Infrared absorption spectra from metastable helium atoms (2[ital s] [sup 3][ital S], 2[ital s] [sup 1][ital S]) and molecules ([ital a] [sup 3][Sigma][sub [ital u]][sup +]) were previously acquired by irradiating dense helium gas near 4.2 K with a pulsed proton beam [R. L. Brooks, J. L. Hunt, and D. W. Tokaryk, J. Chem. Phys. 91, 7408 (1989)]. The molecular spectrum was unusual because the observed rovibrational distribution within the [ital a] [sup 3][Sigma][sub u][sup +] state was far from thermal equilibrium. Three different rovibrational groups were observed: (i) [ital v]=0, [ital N]=1 ( thermal'' molecules); (ii) [ital v]=0, 9[le][ital N][le]21 (rotationally excited molecules); and (iii) 10[le][ital v][le]12, [ital N]=1 (vibrationally excited molecules). In this work, the time evolutions of members of these three molecular populations were studied both during irradiation and in the subsequent afterglow. In addition, the evolution of the 2[ital s] [sup 3][ital S]--2[ital p] [sup 3][ital P] atomic line was investigated. This study quantitatively explores the reaction dynamics of the metastable molecule in the gas phase near 4.2 K. Gas pressures between 100 and 750 Torr were used. Time-resolved data were taken with a transient-digitizer system and summed for several thousand cycles of the pulsed proton beam. The absorption measurements were converted to time-resolved number densities with the aid of theoretical transition moments. The analysis required that the data be fit to the solutions of sets of coupled differential equations with a nonlinear least-squares-fit routine. The results provide insight into the complicated reactions involved in generating the unusual molecular distribution and into the reactions between the metastable molecules, metastable atoms, and the background helium gas.

• OSTI ID: 6381616
• Journal Information: Physical Review A; (United States), Journal Name: Physical Review A; (United States) Vol. 48:1; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

664100* -- Theory of Electronic Structure of Atoms & Molecules-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION SPECTRA
AFTERGLOW
ATOM COLLISIONS
ATOM-MOLECULE COLLISIONS
ATOMS
BEAMS
COLLISIONS
COUPLING
DATA ANALYSIS
DIFFERENTIAL EQUATIONS
DIMERS
ELEMENTS
EMISSION SPECTRA
ENERGY LEVELS
EQUATIONS
EXCITED STATES
FLUIDS
GASES
HELIUM
INFRARED SPECTRA
IRRADIATION
KINETICS
METASTABLE STATES
MOLECULE COLLISIONS
NONMETALS
NUCLEON BEAMS
PARTICLE BEAMS
PROTON BEAMS
PULSES
RARE GASES
REACTION KINETICS
RESOLUTION
SPECTRA
TEMPERATURE RANGE
TEMPERATURE RANGE 0000-0013 K
TIME RESOLUTION
TIMING PROPERTIES