Spectroscopic observation of the preferentially stabilized, linear He•••ICl(X 1Σ+) complex

Spectroscopic features attributed to rovibronic transitions from both the T-shaped and linear He.(ICl)-Cl-35(X) and He.(ICl)-Cl-37(X) ground-state complexes have been recorded in the ICl B (3)Pi(0+)-X (1)Sigma(+), 2-0 and 3-0 spectral regions using laser-induced fluorescence spectroscopy. Experiments performed using varying expansion conditions indicate that the He.(ICl)-Cl-35,37(X) complex with a linear equilibrium orientation lies lower in energy than the separately localized T-shaped isomer even though the transition energies of the T-shaped and linear complexes are shifted by similar to3.5 and similar to14 cm(-1) to higher energy than the (ICl)-Cl-35,37 B-X band origins, respectively. Based on comparison with the excited state theoretical predictions of Waterland [J. Chem. Phys. 92, 4261 (1990)], estimates of the binding energies for the ground state T-shaped and linear He.(ICl)-Cl-35(X) complexes are 17 and 21 cm(-1), respectively, in qualitative agreement with the recently published predictions of 15.2 and 18.3 cm(-1) obtained using high level ab initio theory for the ground state potential energy surface [J. Chem. Phys. 117, 7017 (2002)]. (C) 2003 American Institute of Physics.