Journal
JOURNAL OF MOLECULAR SPECTROSCOPY
Volume 236, Issue 1, Pages 116-126Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jms.2006.01.002
Keywords
NH3; ammonia; far-infrared; submillimeter; global fit; optical heterodyne; frequency; calibration; cavity; etalon; laser locking; metrology
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In this paper, we report 30 THz measurements of ammonia in its excited, nu(2) = 1, inversion state. These measurements include transition frequencies and pressure shifts (where significant enough to be observed). Included in the data are two forbidden and three ro-inversion transitions, as well as 18 transitions never directly measured before. The measurements were made with an all-solid-state, diodelaser, difference-frequency spectrometer. Using an innovative laser-frequency locking scheme, this spectrometer provided accurately determined and continuously tuned THz-frequencies without requiring accurate knowledge of the absolute laser frequencies. The details of the spectrometer's frequency calibration is discussed. A global analysis of NH3 based on the available ground state, nu(2)=1 state, and nu(2)-band transitions was carried out, and the resulting set of recommended molecular effective-Hamiltonian parameters for ammonia is presented. In addition, calculated center frequencies and intensities for all possible transitions up to J = 20 between rotation, inversion, and vibration levels in the ground and nu(2)=1 states are included as supplementary material. (C) 2006 Elsevier Inc. All rights reserved.
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