Knowledge Bank

The He-HCN cluster is a weakly bound cluster with a binding energy of only $9cm-1,a,b$ Previously, two van der waals transitions were reported by electric resonance $spectroscopy.a$ In the present study, a number of new j=1-0 van der waals bending transitions predicted below the dissociation $limitb$ have been observed in 95-125 GHz region with a high sensitivity multi-reflection millimeter wave jet cell. 10 round trip optical paths were used in the measurement. We used a pulsed jet nozzle and the jet cell was evacuated by a diffusion pump. We have measured 13 Q-branch lines up to 1=4 with j=1-0 where l and j are the rotational quantum number of the cluster and the HCN subunit. The lines were fitted to a Hamiltonian expanded using a anisotropic intermolecular potential. The potential function was determined to be $V=-2.2530(43)P1(\cos \theta )-0.665(62)P2(cos\theta )-0.45(17)P3(\cos \theta )$ (in $cm-1$ units)and shows a large anisotropy with respect to the angle $\theta$ between the HCN and the intermolecular cluster axis.