Interpretation and Analysis of Perturbed Spectra of Axially Symmetric Molecules with Applications to Carbon -13 Labelled Trideutero Methyl Fluoride.

The main thrust of this study is the development and testing of an algorithm to fit perturbed vibration -rotation molecular spectra. The algorithm is first developed in a general form and then applied to the vibration-rotation spectra of axially symmetric molecules using simulated data. The 5 (mu)m absorption spectrum of ('13)CD(,3)F is very complex. There are 24 vibrational levels in the region from 1800 cm('-1) to 2250 cm('-1). There are many strong vibrational and rotational resonances linking these states. The states included in this analysis are (nu)(,4)(l(,4) = (+OR-)1), 2(nu)(,2)(l = 0), (nu)(,2) + (nu)(,5)(l(,5) = (+OR-)1), 2(nu)(,5)(l(,5) = 0,(+OR-)2), (nu)(,2) + (nu)(,3)(l = 0), (nu)(,1)(l = 0) and (nu)(,3) + (nu)(,5)(l(,5) = (+OR -)1), all of which lie above 2050 cm('-1). The states omitted in this analysis are (nu)(,2) + (nu)(,6)(l(,6) = (+OR-)1), (nu)(,5) + (nu)(,6)(l(,5) = (+OR-)1,(nu)(,6) = (+OR-)1), 2(nu)(,3)(l = 0), (nu)(,3) + (nu)(,6)(l(,6) = (+OR-)1), and 2(nu)(,6)(l(,6) = 0,(+OR-)2), all of which lie below 2025 cm('-1). These two groups of vibrational states are weakly linked by a higher order vibration-rotation resonance between (nu)(,1) and (nu)(,2) + (nu)(,6)(l(,6) = -1) and a weak vibrational resonance between (nu)(,1) and 2(nu)(,3). The absorption spectrum of ('13)CD(,3)F was recorded at a resolution of 0.018 cm('-1) and deconvolved to an effective resolution of 0.006 cm('-1). The (nu)(,1), 2(nu)(,5)(l(,5) = 0), 2(nu)(,2) and (nu)(,4)(l(,4) = (+OR-)1) bands were analyzed individually to obtain estimates of the molecular parameters of these states. The local and nonlocal resonances were characterized and interaction constants were estimated which gave a qualitative agreement with the observed spectrum. The parameters were then refined using a Hamiltonian model which included all possible interactions from the vibration-rotation Hamiltonian through third order with the restriction that (DELTA)K - (SUMM)(DELTA)l = 0.