GENERAL SYMMETRY SELECTION-RULES FOR THE PHOTOIONIZATION OF POLYATOMIC-MOLECULES

General rovibronic symmetry selection rules, which are applicable to a ny molecular symmetry, have been obtained for the photoionization of p olyatomic molecules. The use of the molecular symmetry groups leads to a particularly transparent derivation. The photoelectron is character ized by a partial wave expansion in the orbital angular momentum quant um number 1. For a given value of 1, one-photon electric dipole transi tions can only occur between neutral and ionic states that obey the ro vibronic symmetry conditions Gamma(rve)(neutral) circle times Gamma(rv e)(ion) superset of Gamma for 1 even and Gamma(rve)(neutral) circle t imes Gamma(rve)(ion) superset of Gamma((S)) for 1 odd, where Gamma((S) ) and Gamma represent the totally symmetric and the antisymmetric rep resentations, respectively. Combined with the well-known angular momen tum conservation selection rule Delta J=J(+)-J=1+3/2, 1+1/2,..., 1-1/2 , 1-3/2 (where J(+) and J represent the total angular momentum quantum number of the ionic and the neutral state between which the photoelec tronic transition occurs), these symmetry selection rules give an over all picture of photoionization in molecules. The formalism, which has also been extended to multiphoton ionization processes, is successfull y applied to the analysis of rotationally resolved photoelectron spect ra of ND4, NH3, C6H6 and H2O.