First Excited and Cationic Ground States of Jet-Cooled 2-Aminopyridine•Ar n (n = 1, 2) Clusters:  Energetics and Structures

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2003-06, Vol.107 (24), p.4826-4828
• Main Authors: Baek, Sun Jong, Choi, Kyo-Won, Choi, Young S, Kim, Sang Kyu
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp026938r

Resonant-enhanced multiphoton ionization (REMPI) and mass-analyzed threshold ionization (MATI) spectra of 2-aminopyridine (2AP−NH2)·Ar n clusters are reported to give the S1−S0 spectral origins of 33 439 and 33 411 cm-1 for the 2AP−NH2·Ar and 2AP−NH2·Ar2 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 (S1) and Ar is estimated to be ∼525 cm-1. Blue-shifts of the 10b2 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.