Ion core structure in (N2O)n+(n=2–8) studied by infrared photodissociation spectroscopy.

IR photodissociation (IRPD) spectra of (N2O)2+•Ar and (N2O)n+ with n=3–8 are measured in the 1000–2300 cm-1 region. The (N2O)2+•Ar ion shows an IRPD band at 1154 cm-1, which can be assigned to the out-of-phase combination of the ν1 vibrations of the N2O components in the N4O2+ ion; the positive charge is delocalized over the two N2O molecules. The geometry optimization and the vibrational analysis at the B3LYP/6-311+G* level show that the N4O2+ ion has a C2h structure with the oxygen ends of the N2O components bonded to each other. The IRPD spectra of the (N2O)n+(n=3–8) ions show three prominent bands at ∼1170, ∼1275, and ∼2235 cm-1. The intensity of the ∼1170 cm-1 band relative to that of the other bands decreases with increasing the cluster size. Therefore, the ∼1170 cm-1 band is ascribed to the N4O2+ dimer ion core and the ∼1275 and ∼2235 cm-1 bands are assigned to the ν1 and ν3 vibrations of solvent N2O molecules, respectively. Since the band of the N4O2+ ion core is located at almost the same position for all the (N2O)n+(n=2–8) clusters, the C2h structure of the dimer ion core does not change so largely by the solvation of N2O molecules, which is quite contrastive to the isoelectronic (CO2)n+ case. [ABSTRACT FROM AUTHOR]