New Determinations of the Vibrational Constants of Li6F and Li6Cl35 by the Molecular Beam Electric Resonance Method

Abstract

New measurements of the vibrational constants of LiF and LiCl were stimulated by the hypothesis of Klemperer and Herschbach that disagreement between infrared and previous molecular beam values of these constants could be explained by a variation in the efficiency of the molecular beam detector with vibrational state. The new molecular beam results rule out this hypothesis because of their agreement with infrared results. These new values are 930±19 cm—1 for Li6F and 705±14 cm—1 for Li6Cl35. The agreement of these values with the infrared results leads to the conclusion that the vibrational states of molecules in the molecular beam source have a Boltzmann distribution. The relative detector efficiency for the vibrational states v=0 and v=1 did not vary when the total efficiency was changed over a range from 0.2 of the maximum value to the maximum. The ratio of the vibrational constants of Li6F and Li7F was found to be 1.06±0.01, in agreement with the value calculated from the ratio of the reduced masses. A rough measurement of the vibrational decay constant between the v=1 and v=0 states gave 65±40 sec—1.