Experimental and theoretical investigations of HeNeI2 trimer.

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(ß1g) 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.

Heterogeneous and hyperfine interactions between valence states of molecular iodine correlating with the I((2)P1/2) + I((2)P1/2) dissociation limit.

Detailed analysis of interactions between all 0g (+), 1u, and 0u (-) weakly bound states of iodine molecule correlating with the I((2)P1/2) + I((2)P1/2) (bb) dissociation limit has been performed. For this purpose, the 0u (-) (bb) state has been described using analysis of rotationally resolved excitation spectra of luminescence from the g0g (-) state populated in a three-step three-color perturbation facilitated excitation scheme via the 0u (-) state. Energies of 41 rovibrational levels, molecular constants, and potential energy curve have been determined. Energy gaps between closest rovibrational levels of the 0u (-) and 0g (+), 1u (bb) states are found to be large, ∼6 cm(-1). However, interaction of all three 0g (+), 1u, and 0u (-) (bb) states has been observed. It has been found that the 0u (-) and 1u electronic states are mixed by heterogeneous interactions, while their mixing with the 0g (+) one is due to hyperfine interactions predominantly. Admixture coefficients and electronic matrix elements of the coupling between the 0g (+) ∼1u, 0g (+)∼0u (-), and 0u (-) ∼1u states have been estimated.