ROTATIONAL PERTURBATIONS IN THE (2+1) REMPI SPECTRUM OF THE RYDBERG STATE [(2)PI(3 2)](C)5D-1G OF I-2/

Partly rotationally resolved (2 + 1) resonance-enhanced multiphoton io nization contour spectra of the vibrational bands corresponding to the [(2) Pi(3/2g)](c)5d;1g <-- <-- X transition in iodine, recorded at ro om temperature, have been analyzed. Irregular band spectral structures could be simulated by assuming rotational line strengths to be depend ent on rotational quantum number in the resonantly excited state at th e two-photon level. The analysis allowed improved rotational constants ((B) over bar(v') and (D) over bar(v')) and corresponding internuclea r distance (r(v')) for the Rydberg state to be evaluated, as well as t he characteristic rotational parameters, (B) over bar'(e) = 0.04047 +/ - 0.00010 cm(-1), alpha'(e) = (1.3 +/- 0.2) X 10(-4) cm(-1) and r'(e) = 2.562 +/- 0.003 Angstrom. The anomalies in the rotational structure are ascribed to perturbation effects due to heterogeneous interaction between an ion-pair state and the Rydberg state. A candidate for the p erturbing state is the D'(2g) state.