Atom—molecule sudden theory of scattering: AB Initio corrections and range of validity of the collision model

The problem of describing atom—molecule vibro-rotational processes, within a sudden picture of scattering, is analyzed in a completely ab initio fashion. The resulting generalized infinite order sudden (GIOS) theory characteristically: (1) emphasizes the role of off-shell sudden T-matrices; (2) leads, from first principles, to corrective terms describing the influence of target motion. It is pointed out that, by means of such corrective terms, it is possible to define β(ⁿ) coefficients, related to the (Δτr_A/Δτr_BC)ⁿ power of (atomic/molecular) characteristic times for the process considered. A numerical analysis of such coefficients then leads to quantitative information on the validity of the sudden picture of energy transfer, for the process investigated. The theory is tested numerically by applying it to a collinear model of vibrational excitation.