Rotation–torsion–vibration term-value mapping for CH3OH: Torsion-mediated doorways and corridors for intermode population transfer

Fourier transform spectroscopy of the CO-stretching band of O-18 methanol

“…This coupling has previously been investigated for the normal and C-13 isotopomers [3][4][5]13], and we now have evidence of such coupling for the O-18 species as well. Again the effect of isotopic tuning comes into play.…”

“…As well, we see in Fig. 6 that the m t = 0 subband origins have a distinct up- Table 4 Molecular constants for the CO-stretching state of CH 3 18 OH from least-squares fits to CO-stretch subband origins a . [9].…”

“…As with the other methanol isotopologues [1][2][3][4][5][6][7]13], several of the CH 3 18 OH m 8 CO-stretching subbands show evidence of perturbations due to intermode interactions, most notably with excited torsional levels of the ground state or with the m 7 in-plane CH 3 -rocking mode [8]. The perturbations can either extend over an entire substate or be strongly localized due to a sharp level-crossing resonance.…”

“…The m 8 band is one of the strongest vibrational bands for methanol, and previous studies for other isotopic species ( [1][2][3][4][5][6][7], for example, and references cited therein) have revealed numerous interesting features of the CO-stretching mode and its interactions with other vibrational states. The closest state to m 8 is the m 7 in-plane CH 3 -rocking mode, which can couple to the CAO stretch via a variety of Coriolis resonances.…”

“…When the wavenumbers for a given series were tabulated in a spreadsheet difference table, educated guesses about the J values could be made from the magnitudes of the first differences, leading in turn to an informed guess about the K value from the starting J value of the series. Since accurate ground-state combination differences were available from the analyses of the far-infrared spectrum of CH 3 18 OH [9,10], corresponding R and P subbranches could be unmistakably linked and the A or E torsional symmetry and torsional quantum number m t established to give the full subband assignment. However, the CO-stretching band has a dense structure and exhibits severe overlapping, as seen in Fig.…”