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 sim;1200ndash;1400thinsp;deg;K and sim;0.1 Torr is mixed with a diluent gas at sim;30ndash;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 thev=0, 1, 2, 3 states in seeded beams of LiF with Ar, NH3, ND3, and SF6as diluents were determined by electric resonance spectroscopy. For Ar as diluent, the LiF vibrational energy has a Boltzmann distribution with a temperature only sim;10percnt; lower than the beam source. For the polyatomic diluents, the LiF vibrational distribution is markedly nonhyphen;Boltzmann. The nominal vibrational temperatureTv, defined by comparing the population of statevto that of the ground state, drops substantially for the highervstates. The vibrational relaxation becomes more pronounced as the source pressure of alkali halide or diluent gas is increased. For the experimental conditions used here,Tvfor thev=3 state drops to sim;2/3 of the source temperature; much stronger relaxation can be expected at higher source pressures.
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