A method to estimate intermolecular potential well depths for species in both ground and excited electronic states

Abstract

The relationship lnσ_M=lnC+[(ε_A*_A*) (ε_MM)]^1/2/kT correlates the cross sections σ_M 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 ε_A*_A* for electronically excited atoms (Na, Ne, Ar, Xe) and electronically excited molecules (I₂, SO₂, CH₃OH, 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 C₅H₉⁺ ion with high vibrational excitation. The correlation also provides an alternate means to measure ground state well depths ε_MM. 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.