Vibrational relaxation in seeded supersonic alkali halide beams

Journal Article · Sat Oct 01 00:00:00 EDT 1977 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.435263· OSTI ID:7297816

Mariella, Jr, R P; Neoh, S K; Herschbach, D R; Klemperer, W

A seeded supersonic beam source for alkali halides is described which can provide high intensity, a narrow velocity distribution, enhanced or reduced translational energy (by choice of diluent mass), low rotational temperature, and partially relaxed vibrational populations. Alkali halide vapor at approx.1200--1400 /sup 0/K and approx.0.1 Torr is mixed with a diluent gas at approx.30--100 Torr and expanded through a pinhole nozzle 0.1 mm in diameter. Velocity analysis of a seeded CsF beam with Ar as the diluent indicates the beam properties conform approximately to the theory of isentropic expansions, with deviations attributable to the relatively low source pressure used. The vibrational populations of the v=0, 1, 2, 3 states in seeded beams of LiF with Ar, NH/sub 3/, ND/sub 3/, and SF/sub 6/ as diluents were determined by electric resonance spectroscopy. For Ar as diluent, the LiF vibrational energy has a Boltzmann distribution with a temperature only approx.10% lower than the beam source. For the polyatomic diluents, the LiF vibrational distribution is markedly non-Boltzmann. The nominal vibrational temperature T/sub v/, defined by comparing the population of state v to that of the ground state, drops substantially for the higher v states. The vibrational relaxation becomes more pronounced as the source pressure of alkali halide or diluent gas is increased. For the experimental conditions used here, T/sub v/ for the v=3 state drops to approx.2/3 of the source temperature; much stronger relaxation can be expected at higher source pressures.

• Research Organization: Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138
• OSTI ID: 7297816
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 67:7; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640301* -- Atomic
Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKALI METAL COMPOUNDS
ARGON
BEAMS
CESIUM COMPOUNDS
CESIUM FLUORIDES
ELEMENTS
ENERGY LEVELS
EXCITED STATES
FLUID FLOW
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
LITHIUM COMPOUNDS
LITHIUM FLUORIDES
LITHIUM HALIDES
MOLECULAR BEAMS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
RARE GASES
RELAXATION
SULFUR COMPOUNDS
SULFUR FLUORIDES
SUPERSONIC FLOW
VELOCITY
VIBRATIONAL STATES