INFRARED-SPECTROSCOPY OF THE AMIDOGEN ION, NH2+

The absorption spectrum of NH2+ has been recorded continuously between 3500 and 2900 cm(-1) with a difference frequency laser spectrometer a long with the velocity modulation technique. The molecular ions were p roduced in the positive column of an ac glow discharge with a gas mixt ure of N-2/H-2/He in a ratio of around 1/1/100 with a total pressure o f similar to 7 Torr. In view of the very low harrier to linearity (155 cm(-1)) and the high bending vibrational states involved, the observe d spectrum was analyzed using the Hamiltonian for linear molecules. Th e choice of this model is discussed in relation to the previous experi mental results and ab initio calculations. Four hot bands have been as signed: 2v(2)(0) + v(3) <-- 2v(2)(0), v(1) + v(3) <-- v(1), v(1) + v(2 ) + v(3) <-- v(1) + v(2), and 2v(1) + v(3) <-- 2v(1). The matrix eleme nts of the Hamiltonian used for the analysis of the rotational fine st ructure of the excited degenerate bending vibrational states of a line ar molecule in a triplet electronic state are presented. The resultant rotational and vibrational constants are discussed. (C) 1996 Academic Press, Inc.