COMPLEX ANGULAR-MOMENTUM ANALYSIS OF RESONANCE SCATTERING IN THE CL-]CLH+CL REACTION(HCL)

Resonance effects in the differential cross sections of the Cl+HCl(ups ilon',j)-->ClH(upsilon',j')+Cl reaction are analyzed using Regge pole and complex angular momentum (CAM) techniques. This is the first detai led application of CAM theory to reactive molecular scattering. The ro vibrational transitions studied are upsilon-1, j=5-->upsilon'=0, j'=15 , and upsilon=1, j=5-->upsilon'=1, j'=5 at total energies E=0.66, 0.68 , 0.70 eV. The CAM theory expresses the scattering amplitude as a back ground subamplitude plus a pole subamplitude. The uniform (and nonunif orm) semiclassical evaluation of the background subamplitude is discus sed. It is necessary to include explicitly the resonance Regge pole in the semiclassical theory because it has a small imaginary part. We de rive a new generic semiclassical formula, involving the complementary error function for the resonance angular scattering. The position and residue of the resonance Regge pole at each E are extracted numericall y from scattering matrix elements calculated by the centrifugal sudden hyperspherical (CSH) quantum scattering method. There is good agreeme nt between the semiclassical CAM and CSH angular distributions. Howeve r, the latter involve summing a partial wave (PW) series with a large number of numerically significant terms-as a result the PW computation s provide no physical insight. We also show that a simple semiclassica l optical model becomes inaccurate when the rotational period of the C lHCl complex is comparable to the resonance lifetime. We derive a new ''sticky'' optical model which allows for rotation of the complex, All our calculations use the Bondi-Connor-Manz-Romelt semiempirical poten tial energy surface. (C) 1995 American Institute of Physics.