Photoelectron spectra of Ar(n).(IHI)- (n = 0-6, 12, 20), a theoretical study

The effects of the introduction of argon atoms on the photoelectron (PE) spectra of Ar(n).(IHI)- with n = 0-6, 12, and 20 are investigated. Time-independent quantum simulations of the spectra using a rigid cage approximation and allowing the motion of the IHI core are performed. As in our previous classical studies on this system, we find an increase in the confinement of the hydrogen atom motion as the number of argon atoms is increased. Comparison of the quantum and classical descriptions of this confinement provides evidence of the importance of quantum mechanical effects in this system. Three approaches are used to calculate the spectrum of the bare (IHI)- system. Excellent agreement is found between the simulated peaks in the = 2 region using a full three-dimensional quantum simulation of the PE spectrum, those from the corresponding experimental threshold photodetachment spectrum and those obtained by employing an adiabatic separation of the motions of the hydrogen and the iodine atoms. This provides further confirmation that these peaks are the result of motions of the iodine atoms. Simulations of the Ar(n).(IHI)- PE spectra show a shift of the spectra to lower electron kinetic energies as the number of argon atoms is increased. Similar shifts are found in the experimental spectra and in our previous study of this system using classical trajectory simulations. It is also found that the I-I motion mainly affects the spectrum features, whereas the progressions associated with hindered rotor transitions are less affected. Finally, an increase in the intensity of the = 0 peak and an accumulation of transitions in the low-frequency hindered rotor region with increasing number of argon atoms are observed.