Vibronic spectrum of the Ag(NH3)2 complex

We report observation of the resonantly enhanced two-photon ionization (R2PI) spectrum of the Ag(NH3)2 complex formed in a free jet. The origin of the A–X band system is located 947 cm−1 lower than that of AgNH3 and shifted from the corresponding Ag (5p2P1/2–5s2S) transition by 9089 cm−1. This indicates that the stabilization of the excited silver atom by the second ammonia molecule is much smaller than that caused by the first one. The well-resolved vibrational progressions are characterized by three vibrational frequencies, 197, 67, and 375 cm−1. We have assigned these to the (AgNH3)–NH3 stretching, (AgNH3)–NH3 bending, and Ag–NH3 stretching modes, respectively, based on the ab initio structure of Dubois et al. [Chem. Phys. Lett. 323, 1 (2000)]. The R2PI signal suddenly disappears ∼500 cm−1 above the origin, which indicates that some nonradiative transition takes place.