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

Abstract

a b s t r a c tStimulated by recent THz measurements of the methanol spectrum in one of our laboratories, undertaken in support of NASA programs related to the Herschel Space Observatory (HSO) and the Atacama Large Millimeter Array (ALMA), we have carried out a global analysis of available microwave and high-resolution infrared data for the first three torsional states (m t = 0, 1, 2), and for J values up to 30. This global fit of approximately 5600 frequency measurements and 19 000 Fourier transform far infrared (FTFIR) wavenumber measurements to 119 parameters reaches the estimated experimental measurement accuracy for the FTFIR transitions, and about twice the estimated experimental measurement accuracy for the microwave, submillimeter-wave, and terahertz transitions. The present fit is essentially a continuation of our earlier work, but we have greatly expanded our previous data set and have added a large number of new torsion-rotation interaction terms to the Hamiltonian in our previously used computer program. The results, together with a number of calculated (but unmeasured) transitions, including their line strength, estimated uncertainty, and lower state energy, are made available in the supplementary material as a database formatted to be useful for astronomical searches. Some discussion of several open spectroscopic problems, e.g., (i) an improved notation for the numerous parameters in the torsion-rotation Hamiltonian, (ii) possible causes of the failure to fit frequency measurements to the estimated measurement uncertainty, and (iii) pitfalls to be avoided when intercomparing apparently identical parameters from the internal axis method and the rho axis method are also given.

Rotational spectroscopy, tentative interstellar detection, and chemical modeling of N-methylformamide

“…(b) Parameter nomenclature based on the subscript procedures of Xu et al (2008) (c) {A, B, C} = ABC + CBA, {A, B} = AB + BA. The product of the operator in the third column of a given row and the parameter in the second column of that row gives the term actually used in the torsion-rotation Hamiltonian of the program, except for F, ρ and A RAM , which occur in the Hamiltonian in the form F(p α − ρP a ) 2 + A RAM P 2 a .…”

Sensitivity of transitions in internal rotor molecules to a possible variation of the proton-to-electron mass ratio

“…It was therefore suggested by Lees [22] to refer to E1 and E2 levels as E levels where the sign of K distinguishes the two symmetries. The eigenvalues of the torsional Hamiltonian for methanol [23], acetaldehyde [24], and acetic acid [25] are depicted in Fig. 2 [16] for the A, E1, and E2 torsional states, respectively.…”

“…We have calculated the sensitivity coefficients of many (>1000) transitions in methanol, acetaldehyde, acetamide, methyl formate, and acetic acid, using the constants listed in Refs. [23][24][25]29,30], respectively. In Table II sensitivity coefficients of selected transitions in the vibrational ground state (ν t = 0) of these molecules are listed.…”

“…With the help of Fig. 7, it is straightforward to select transitions that are likely to have a Energy (cm Table III and the molecular constants of methanol [23]. The highest sensitivities are expected when torsional energy is converted into rotational energy or vice versa, that is, when the two curves cross.…”

Millimeter wave and terahertz spectra and global fit of torsion–rotation transitions in the ground, first and second excited torsional states of 13 CH 3 OH methanol

“…Also, as was again found earlier in the fitting for the parent species [18], the rms deviation for the MW lines in Table 1 To properly diagnose this problem, the fitting domain should really be expanded to include the higher torsional levels and the low-lying vibrational states, which represents a rather substantial undertaking for the future.…”