First excited and cationic ground states of jet-cooled 2-Aminopyridine center dot Ar-n (n=1, 2) clusters: Energetics and structures

Abstract

Resonant-enhanced multiphoton ionization (REMPI) and mass-analyzed threshold ionization (MATI) spectra of 2-aminopyridine (2AP-NH2)Ar-. clusters are reported to give the S-1-S-0 spectral origins of 33439 and 33411 cm(-1) for the 2AP-(NH2Ar)-Ar-. and 2AP-(NH2Ar2)-Ar-. clusters, respectively, and also their respective adiabatic ionization energies of 8.0881 +/- 0.0021 and 8.0676 +/- 0.0020 eV. The upper bound for the van der Waals binding energy of 2AP-NH2 (S-1) and Ar is estimated to be similar to525 cm(-1). Blue-shifts of the 10b(2) out-of-plane vibrational mode by clustering provide the evidence of one atom-caging effect in the vibrational motion. Van der Waals modes at internal energies of 21 and 13 cm(-1) are weakly observed in MATI spectra of 2AP-NH2+.Ar and 2AP-NH2+.Ar2 clusters, respectively, indicating that the cluster ionization is accompanied by the minimum structural change. Ab initio calculated cluster structures are also reported.