Photodetachment and Tunneling Dissociation of Cryogenic Double-Rydberg Anions NH 4 .

The Rydberg radical NH 4 and the double Rydberg anion (DRA) NH 4 - have long aroused researchers' interests due to their potential for exploring the reaction dynamics of the H + NH 3 → H 2 + NH 2 reaction, a prototypical penta-atomic system. In this study, we present high-resolution photodetachment spectroscopy of DRA NH 4 - and ion-molecule complex H - (NH 3 ). We observed multiple new photodetachment channels of DRA NH 4 - . The energy level of the excited state (3p 2 T 2 ) of the Rydberg radical NH 4 was determined to be 15052(94) cm -1 , in excellent agreement with the principal Schüler band (15061.61 cm -1 ). Additionally, we observed the tunneling dissociation of NH 4 - in a cryogenic ion trap with its dissociation lifetime determined to be 19(2) ms.