The anharmonic potential energy surface of methyl fluoride

High resolution IR spectrum of the ν8 band of CH2DF: analysis of the interactions with the near vibrational levels

“…Accurate spectroscopic constants on methyl fluoride and its isotopologues are of considerable importance for the determination of the equilibrium structure [1], ab initio cubic force field [2] and anharmonic potential energy surface [3]. Among the different isotopologues of this molecule, CH 2 DF is the least characterized.…”

The molecular potential energy surface and vibrational energy levels of methyl fluoride. Part II

“…Methyl fluoride is a very important prototype for experimental and theoretical studies in spectroscopy, [1][2][3][4][5][6][7][8][9][10] structure and bonding, [11][12][13][14][15][16][17] intramolecular dynamics 3,4,6,[17][18][19][20] and reaction dynamics. 17,[21][22][23] The spectroscopy and dynamics of a five-atom molecule such as methyl fluoride present a number of major challenges to both theory and experiment.…”

“…Most earlier ab initio studies of the potential energy surface of methyl fluoride have taken one of two approaches: the first involves exploring, at a modest level of theory, a region close to the equilibrium configuration that can be described adequately with a low-order Taylor expansion in normal mode or other internal coordinates; 2,11,13,15 the second approach explores, at a high level of theory, a few critical points on the potential energy surface. 14,16,17,21,22 A third approach, taken by Luckhaus and Quack, 4 was to focus on the three-dimensional potential energy surface of the C-H chromophore in CHD 2 F. Here we will consider, using a relatively high level of theory, two reduced subspaces of the methyl fluoride potential energy surface (five-dimensional (5D) bending and fourdimensional (4D) stretching) each including large distortions from the equilibrium geometry.…”

“…On the other hand, the ability to compute vibration-rotation energy levels (and transition intensities) opens up the possibility of extracting detailed information on the potential energy surface from experimental high resolution spectroscopic data. 33 Previous efforts to derive potential energy surface information for methyl fluoride from spectroscopic data 12,15 have relied on perturbation theory or other approximate methods to compute ro-vibrational properties. The application of perturbation theory to methyl fluoride (and its isotopomers) is severely complicated by the presence of many Fermi and Coriolis resonances.…”

“…The application of perturbation theory to methyl fluoride (and its isotopomers) is severely complicated by the presence of many Fermi and Coriolis resonances. 15 In this context, it is important to note that methyl fluoride is an important prototype for developing and testing new ab initio electronic structure methods. 13,34 High resolution spectroscopic data afford the most stringent tests for comparison with ro-vibrational properties computed from an ab initio molecular potential energy surface.…”