High-resolution photoelectron spectroscopy of HI and DI: Experimental and theoretical analysis of the A ~2SIGMA~+ ion system

摘要

A combined high-resolution (6 me V) HeI photoelectron (PE) and ab initio theoretical study of the A ~2SIGMA~+ ion system of HI and DI has been conducted to elucidate the origin of the peculiar "holelike" feature in the vibrational distribution found in the high-resolution (6 meV) threshold photoelectron (TPE) spectrum of HI. The PE and TPE spectra were found to yield essentially identical results. Ab inito potential energy curves for the low-lying cationic states of HI have been calculated for the first time with and without spin-orbit contributions included. It has been found that the adiabatic A ~2 SIGMA~+ state of HI~+ is strongly predissociated due to spin-orbit coupling with the ~4SIGMA~-, 2SIGMA~-, and ~4PI repulsive state leading to a complex set of adiabatic curves. It is shown that the adiabatic A ~2 SIGMA_(1/2)~+ state is only slightly bound (by 260 cm~(-1) after suitable adjustments of the positions of the various repulsive potentials relative to that of the A state are made based on observed atomic spectral data) and should support at most one vibrational level in both HI~+. However, using the complex rotational method, it was possible to calculate the energies, predissoication linewidths, and rotational constants of a number of nonstationary vibrational levels (or resonances) of the A ~2SIGMA_(1/2)~+ state. Reasonably good agreement has been found between experiment and theory. The observed 'hole" in the TPE and PE spectra is attributed to the fact that the stability of the upsilon~ =1 and 2 levels is notably less than for upsilon~+ =0 in the A ~2SIGMA_(1/2)~+ state of both HI~+ and DI~+.