Spectroscopy and dynamics of He2Cl2: A quantum liquid cluster?

Abstract

The two color pump–probe technique has been used to study the B←X excitation spectrum and vibrational predissociation product state distribution of He2Cl2. Although the excitation spectrum of the complex shows distinct rotational structure and the expected rotational temperature of the complex is below 1 K, we are unable to even approximately reproduce the band shape with a rigid rotor analysis. The main dissociation channel for the complex involves the transfer of two quanta of Cl2 stretching motion, almost certainly in a sequential process. The product Cl2 rotational distribution is remarkably similar to that of HeCl2 undergoing Δv=−2 dissociation. One reason for the similarity between the HeCl2 and He2Cl2 dissociation product state distributions is that vibrational excitation of the HeCl2 van der Waals modes has little effect on the product state distribution. He2Cl2 provides an example of an extremely floppy, liquidlike cluster whose spectroscopy and dynamics can be studied with detailed state resolution.