METHOD TO ESTIMATE INTER-MOLECULAR POTENTIAL WELL DEPTHS FOR SPECIES IN BOTH GROUND AND EXCITED ELECTRONIC STATES

The relationship 1nσM = 1nC + [(εA* A*) (εMM)]1/2/kT correlates the cross sections σM for a state change A*→B induced by a series of added M gases with the intermolecular potential well depths for A*...A* pairs and M...M pairs. This correlation is used with literature data concerning A*→B to deduce εA* A* for electronically excited atoms (Na, Ne, Ar, Xe) and electronically excited molecules (I2, SO2, CH 3OH, glyoxal, propynal, benzene). The well depths are generally observed to exceed the ground state values by factors of 2-10. Large well depths are also observed for sec -butyl radicals and for the C5H 9+ ion with high vibrational excitation. The correlation also provides an alternate means to measure ground state well depths εMM. In cases where secure comparisons are available, the well depths so derived usually lie within 20% of values found from transport measurements or virial coefficients. The correlation seems a useful alternative to empirical estimating procedures when data from conventional methods are not available. © 1979 American Institute of Physics.