PNNL

Abstract

We report a joint spectroscopic and theoretical study probing spin-orbit coupling (SOC) in a variety of molecular complexes between an iodine atom and a ligand (L) with L ranging from Ar, HF to formic/acetic acids, and glycine/N-methylated glycine derivatives. Cryogenic photoelectron spectroscopy of L·I– (L = HCOOH, CH3COOH) reveals three distinct peaks, identified as three SOC states, denoted as X(1/2), A(3/2), and B(1/2) for the corresponding neutrals. The X and A separation ?EXA is measured to be 0.10 eV for both, whereas the X and B gap ?EXB is 0.98 and 0.97 eV for formic and acetic acid, respectively. These new ?EXA values are compared with the previously reported values for the molecular complexes L·I• with L = Ar, HF, glycine and N-methylated glycines. All together these complexes encompass a diversity of intermolecular interactions, from van der Waals to weak and strong hydrogen bonding. While the ?EXB remains similar, the ?EXA is shown to be extremely sensitive to the type of ligands and interactions, spanning from 5 meV to 150 meV. High-level relativistic quantum calculations including explicit SOC formulism nicely reproduce all experimental SOC splitting. A direct correlation between the magnitude of ?EXA with the intermolecular interaction strength or bond distance of the neutral complexes ? the stronger interaction (shorter bond length), the larger of the splitting, is established.