Millimeter-Wave Spectra and Global Torsion–Rotation Analysis for the CH3OD Isotopomer of Methanol

The millimeter-wave spectrum of perdeuterated methanol, CD3OD

“…The torsion-rotation model included 44 adjustable parameters up to terms of the sixth order in the torsion-rotation operators. There is good agreement and self-consistency among the final parameter sets obtained here for CD 3 OD and previously for CH 3 OH [24,25], 13 CH 3 OH [26], CD 3 OH [27], and CH 3 OD [28]. This reinforces our confidence that the fitting procedure is welldefined, that the right minima are being found in the leastsquares fits, and that the parameter reliability is sufficient to justify meaningful comparative analysis.…”

“…The ''abnormal feature'' can be attributed to the fact that accidental near-energy-degeneracies in CD 3 OD are a combination of what we have observed in CD 3 OH between the K ¼ 0 and K ¼ 2 E levels for v t ¼ 0 [27] and in CH 3 OD between the K ¼ 0 and K ¼ À1 E levels for v t ¼ 0 [28], resulting from partial cancellation of torsional and K-rotational energies. Because these states are coupled by the DK ¼ 1 and 2 asymmetry matrix elements of the Hamiltonian, their internal asymmetry shifts are particularly large.…”

“…Our method of analysis has been described and applied before [24][25][26][27][28]. Using a computer program (I. Kleiner and M. Godefroid, private communication) based on the formalism in [29], we aim to achieve global fits of all observed transitions to within the assigned experimental accuracies over quantum number ranges sufficient for rigorous tests of the existing one-dimensional model.…”

Torsion–rotation global analysis of the first three torsional states (νt=0, 1, 2) and terahertz database for methanol

“…Refs. [1][2][3][4][5][6][7][8] are associated in one way or another with the laboratory at the University of New Brunswick in Canada, while Refs. [9][10][11][12][13][14][15][16][17][18][19][20][21][22] are representative torsion-rotation fits from other laboratories.…”

“…These two levels are well above the top of the barrier at V 3 = 374 cm À1 , but they are still well below the lowest small-amplitude vibration m 8 near 1034 cm À1 (with A and E components near 1162 and 1171 cm À1 , respectively, when measured from the bottom of the torsional well [25]). Thus, it should in principle be possible to fit torsion-rotation states of the first three torsional levels using the same torsion-rotation Hamiltonian as was used previously [1][2][3][4][5][6][7][8]. Nevertheless, new difficulties arise, since an increase in torsional excitation leads to more level crossings and perturbations, as well as to a denser spectrum with more line overlap and more anomalous intensity variation within branches (compared to that expected for a rigid molecule).…”