Rotational structure in the asymmetric OH stretch of Cs+(H2O)Ar

Evaporative cooling, which is the usual mode of formation for many ion-molecule complexes, typically results in high internal energies. This in turn leads to a broadening of vibrational or vibronic spectra of these species. By incorporating argon into the nascent ion cluster, it is possible to significantly reduce the internal energy and thus simplify the spectra. This approach has been applied to the Cs+(H2O) cluster ion. The binding of argon lowers the internal energy to an effective temperature of 125 K. Rotational structure in the asymmetric stretch can be analyzed to conclude that the structure of Cs+(H2O)Ar is quasi-linear with the heavy atoms in an Ar-Cs+-O configuration and the two hydrogen atoms symmetrically displaced off-axis, pointing away from the ion. (C) 2002 American Institute of Physics.