Experimental and theoretical investigations of HeNeI2 trimer.

Abstract

We report on the results of spectroscopic studies of the HeNeI2 van der Waals trimer using the two-step two-color HeNeI2(E0g +, vE = 0-3 ←hν2B0u +, vB = 19 ←hν1X0g +, vX = 0) excitation scheme. The excitation spectra of the HeNeI2(B, E) decay product luminescence and the luminescence spectra of I2 ion-pair states formed after HeNeI2(E) decay have been recorded and analyzed. The HeNeI2(X, B, E) binding energies have been estimated to be less than 111.8 cm-1, 101.6 cm-1, and 117.9 cm-1, respectively. The HeNeI2(B, vB) state decay has been found to be sequential with the formation of the HeI2(B, vB - 1) and NeI2(B, vB - 1) complexes without intermolecular excitation at the first step. An analysis of the HeNeI2(E) decay process based on the relative probabilities of the I2(D0u +) and I2(β1g) formation after decay, as well as vibrational populations of these states obtained from luminescence spectra, has also been performed. Calculations of the HeNeI2(X, B) vibrational energies using potential energy surfaces (PESs) of HeNeI2(X, B) constructed as a sum of the HeNe, HeI2, and NeI2 potentials have been carried out. The values obtained agree well with the experimental estimations, and the observed transitions can be ascribed to the HeNeI2 trimer of a tetrahedral geometry. Besides, a comparison of the PES constructed as a sum of the coupled-cluster single double triple [CCSD(T)] potentials with the PES based on the "direct" CCSD(T) calculations has been performed for the HeNeI2(X) trimer to verify the applicability of this representation to the trimer under study.