The entry is based on a line list file provided by L.-H. Xu from the review
(1) L.-H. Xu and F. J. Lovas, 1997, J. Phys. Chem. Ref. Data 26, 17.
Details on the RAM (RHO axis method) and fitting program employed to reduce the data is available in
(2) L.-H. Xu, M. S. Walsh, and R. M. Lees, 1996, J. Mol. Spectrosc. 179, 269 and references therein.
These two papers also give details on the extensive data sets considered in the fits. Because of the internal rotation (torsion), torsion-rotation interaction, and large effects of centrifugal distortion, global modeling of the methanol spectrum is a challenging task. Nevertheless, restricting the data set to v_t = 0, 1, J_max = 20, and K_max = 14, the input data was reproduced within experimental uncertainties. Very small experimental uncertainties have been set to 50 kHz for most of the microwave lines in the fit.
Certain prediction, in particular those of higher J, may be found outside three times the uncertainties. However, because of the large body of transitions observed by FTFIR spectroscopy, it is expected that these deviations are within 6 MHz, an uncertainty value assigned to the FTFIR data).
Note: The current entry is essentially identical to the first one, except that now intensities at 300 K are available. In the absence of suffiently extensitive energies in the catalog file or in a separate energy file, partition function values were scaled from those of the ¹⁸O isotopolog, see e034504.cat. Values scaled from the main species differ only slightly. Please note also that we employed here g_I = 1, not 4 as for the main and ¹⁸O isotopologs. The quantum number format has been adjusted to the spcat format, however, the quantum numbers were retained (except that "a" signal a K value below –9.
The quantum numbers given are those of (1) and (2), but slightly rearranged for lay-out reasons. They are
J, (sign)K_a, K_c, (parity), immediately followed by v_t.
The parities + and – refer to A+ and A – states; while states with no parity designation refer to E symmetry. A signed value of K_a is used to differentiate (+)E₁ from (–)E₂ states. It should be emphasized that E₁ and E₂ states belong to the same E symmetry species.
As usual, the energies in the catalog entry are given with respect to the lowest rotational level (0₀₀ of the v_t = 0, A state) which is defined as zero.
The energies given in the documentation refer to the 0₀₀ rotational levels of the
v_t = 0, A and E states and the v_t = 1, E and A states, respectively.
The dipole moment is assumed to be the same as for the main isotopmer, see e032504.cat.
Note: The current entry takes into account contributions of the permanent dipole moment only ! Torsional or rotational dependences as well as changes in the dipole moment with torsional state have not yet been determined – or only to an insufficient amount. The effects of these contributions may be non-negligible in certain instances.