STERIC PROPERTIES OF THE REACTIVE SYSTEM CA(1D2) + CH3F(JKM) -] CAF(A) + CH3

The steric effect of the chemiluminescent CaF(A2-PI) channel from the reaction of Ca(1D2) + CH3F(JKM = 111) --> CaF + CH3 has been investigated employing a state-selected and oriented CH3F molecular beam. Total chemiluminescent cross sections are measured as a function of the collision energy. Deconvoluted excitation functions are obtained which follow the energy dependence of a modified Eu excitation function. The steric effect turns out to increase with increasing energy. A tentative explanation for the energy dependence of the steric effect is proposed in terms of a reorientation of the initially oriented CH3F axis due to long-range interaction. Calculations based on a quadrupole-dipole plus a quadrupole-quadrupole potential surface for the excited Ca(1D2) and the polar CH3F system show a relatively strong anisotropy toward the F side of the CH3F molecule at fairly long atom-molecule distances (5-10 angstrom).