Knowledge Bank

High resolution near infrared spectra of the $vHCL=1\leftarrow 0$ fundamental stretch in and $Ar2HCl$ and $Ar3HCl$ have been characterized using a slit-jet infrared spectrometer. Analysis of the jet cooled, rotationally resolved spectra i) permit unambigous identification of the cluster size, ii) provide vibrationally averaged geometries in the $vHCL=1$ excited, state, and iii) allow the vibrational shift of the HCl chromophore to be measured as a function of the number of Aar atoms in the complex. The equilibrium structures of the $ArnHCl(n=1-3)$ clusters calculated using accurate Ar-Ar and Ar-HCl pair potentials are consistent with the vibrationally averaged structures inferred spectroscopically. The vibrational redshifts for the $ArnHCl(n=l-3)$ reflect a near-linear dependence on the number of Ar atoms, which is qualitatively reproduced by simple classical calculations of the $vHCL=0$ and 1 pairwise additive potential surfaces. Finally, predictions of the HCl matrix shifts in a relaxed fee lattice of Ar atoms significantly overshoot the matrix value and indicate an appreciable sensitivity to non-nearest neighbors in $2nd,3rd$ and higher order solvation shells.