Atomic Resonance and Scattering

Contains reports on nine research projects.U.S. Energy Research and Development Administration (Contract EG-77-S-02-4370)U. S. Air Force - Office of Scientific Research (Contract F44620-72-C-0057)Joint Services Electronics Program (Contract DAAB07-76-C-1400)National Science Foundation (Grant PHY75-15421-AO1)National Science Foundation (Grant PHY77-09155)National Science Foundation (Grant CHE76-81750)U. S. Air Force - Office of Scientific Research (Grant AFOSR-76-2972A

ACCURATE DISSOCIATION ENERGIES FROM ROTATIONAL PREDISSOCIATION AND LONG-RANGE FORCES: B 1Π^{1}\Pi LiH

$^{1}$ R.B. Bernstein, Phys. Rev. Letters 16, 385 (1966). $^{2}$ For a list, see W. C. Stwalley, Chem. Phys. Letters 7, 600 (1970). $^{3}$ R. Velasco, Can. J. Phys. 35, 1204 (1957).""Author Institution: Department of Chemistry, University of Iowa$Bernstein^{1}$ pointed out in 1966 that the centrifugal barriers of the effective potentials governing rotational predissociation were simply obtainable if the ordinary potential could be expressed as V = D_{0} - C/r^{n}. \eqno{(1)}. He (and $others^{2}$) then used these formulas with predissociation data to obtain the constants $D_{0}$ and C for several diatomic molecules, with known long-range values of n. Unfortunately, it now appears that the centrifugal barriers considered in these cases were not at sufficiently large distances for (1) to hold. A search of the rotational predissociation literature produced a $case^{3}$ clearly in the long-range region: v = 2 of B $^{1}\Pi$ LiH. Since we have long-range predissociation in only a single vibrational level, we have chosen to calculate the long-range forces accurately and then use the predissociation data to obtain a precise dissociation limit (with respect to v = 0, J = 0 in the ground state). The effect of higher inverse power terms and tunnelling has also been considered. Our value for the dissociation limit (34 $492.8 \pm 0.5 cm^{-1}$) may be compared with the value given by $Velasco^{3}$ (34 $495 \pm 2 cm^{-1})$. If the width of either J = 2 or 3 of v = 2 were known even roughly, the dissociation limit uncertainty could be reduced to $\mathop {<}\kern -8pt {\vphantom {1 \over 2}}^{\sim} 0.2 cm^{-1}$

THE POTENTIAL ENERGY CURVES FOR THE X1Σ+X^{1}\Sigma^{+}, A1Σ+A^{1}\Sigma^{+} AND B1ΠB^{1}\Pi STATES OF LiH

$^{1}$K. R. Way and W. C. Stwalley, J. Chem. Phys. 59, 5298 (1973).Author Institution: Department of Chemistry, University of Iowa; Dapartment of Chemisty, Wartburg CollegeInformation (primarily spectroscopic) concerning the potential energy curves for the $B^{1}$, A and X states of LiH (in various isotopic combinations) will be surveyed and ``best” potentials proposed. A study of the implications of these potentials, e.g., r the frequencies and intensities of A-X emission to high vibrationa1 levels in the ground state, is in progress and may also be presented