Collision-Induced Dissociation of Cesium Iodide Cluster Ions. Scattering Angular Distribution and Excitation Mechanism

Abstract

Collision-induced dissociation (CID) of cesium iodide cluster ions was investigated at kiloelectronvolt laboratory translational energy using “light” (H 2 ,D 2, and He) and “heavy” (Ne, Ar, and Xe) collision gases. Substantial translational energy losses were observed with light targets, as was the case with polypeptide ions with similar masses reported previously. In the present case, the large energy losses were mainly due to the elastic energy transfer to the targets. From the translational energy profiles of CID product ions, energetic and dynamic data, and, in particular, the scattering angular distribution, were obtained. The angular distributions obtained with H2 ,D 2, and He were virtually identical at the same center-of-mass translational energy while the one with Ne was different. This suggested that the energy transfer mechanism with light targets might be different from that with heavy ones. Theoretical calculations with a binary collision model could explain the angular distributions with Ne, suggesting that vibrational excitation via momentum transfer is a possible candidate mechanism. Even though the angular distributions could not be determined for CID with Xe or Ar collision gases, the same conclusion can be made based on the basis of the magnitudes of the translational energy loss. On the other hand, those with light targets could not be explained with the above model indicating the dominance of vibronic excitation.