ROTATIONALLY RESOLVED SPECTROSCOPY OF THE C-X BAND OF (NH3)-N-15 BY INFRARED-ULTRAVIOLET DOUBLE-RESONANCE

Double resonance measurements on (NH3)-N-15 in a free expansion jet are reported. These were carried out using a continuous wave (CW) CO2 laser and a pulsed ultraviolet (UV) laser system. Infrared radiation was used to prepare molecules in individual rotational levels of the upsilon(2) = 1 vibrational state of the electronic ground state of [N-15]ammonia. These molecules were then photoionized via transitions of the ($) over tilde C-($) over tilde X band in a (2 + 1) process using the doubled output of a pulsed dye laser. The ion signal was detected using a time of flight mass spectrometer. Two known coincidences between CO2 laser lines and individual rovibrational transitions of (NH3)-N-15 were used to populate the (J, K) = (5, 4) and (3, 0) symmetric levels of upsilon(2) = 1. Double resonance signals corresponding to O, P, Q, R, and S branch two photon transitions in the ($) over tilde C'-($) over tilde X band were observed and measured accurately. These data were augmented by conventional (2 + 1) REMPI measurements on the 2(0)(0), 2(0)(1), and 2(0)(2) sub-bands of (NH3)-N-15. A complete set of molecular parameters for the upsilon(2) = 0, 1, and 2 levels of the ($) over tilde C' state was calculated from these data. The results represent the most detailed information so far produced over the ($) over tilde C' state of ammonia. The relevance of these experiments for the investigation of molecular clusters produced in a free expansion jet is discussed.