Knowledge Bank

The tetrahedral ammonium ion has two triply-degenerate infrared-active fundamentals. In 1983, Crofton and Oka; and Schafer, Begemann, Gudeman and Saykally observed the $\nu 3$ fundamental of $NH4-$ in glow discharges. Several subsequent studies have been reported, but only one concerns the other IR-active fundamental. In this work, more than thirty new lines in the $\nu 4$ band of $NH4+$ are reported, together with the first detection of the same band of $ND4+$ These ammonium ions were observed in a water-cooled hollow cathode discharge with a diode laser spectrometer. A program was written to fit the spectra to fourth order based upon the spherical top Hamiltonian of Robierte et al. and using an uncoupled basis set.