A combined experimental/theoretical investigation of the He + ICl interactions: Determination of the binding energies of the T-shaped and linear He⋯I35Cl(X,v″ = 0) conformers

A simple model based on the assumption of a thermodynamic equilibrium between the populations of the T-shaped and linear He⋯I35Cl(X,v″ = 0) complexes stabilized in a supersonic expansion is utilized to estimate the relative binding energies of the ground state conformers. In this model, the relative intensities of the laser-induced fluorescence features, attributed to transitions of each conformer, are used to track changes in the populations along the expansion. The relative intensities of the features and the I35Cl(X,v″ = 0) rotational temperatures measured at each distance are fit to ratios of the quantum mechanical partition functions for the T-shaped and linear complexes. These are used to determine the difference between the binding energies of the two conformers. The linear He⋯I35Cl(X,v″ = 0) complex is estimated to be 2.5(6) cm−1 more strongly bound than the T-shaped conformer. The validity of this model was in part confirmed by performing the analysis on calculated ro-vibronic spectra of He⋯I35Cl, where the J″ = 0 binding energies of the ground state conformers are known. The results from high-resolution action and two-color pump–probe spectroscopy experiments reveal that the binding energy of the linear He⋯I35Cl(X,v″ = 0) conformer is precisely 22.0(2) cm−1. The binding energy of the T-shaped He⋯I35Cl(X,v″ = 0) conformer is then 19.5(6) cm−1.