Methyl Alcohol. I. Microwave Spectrum

Methanol is one of the simplest molecules that undergo torsional oscillations, and so it has been extensively studied in the gas phase by various spectroscopic techniques. At 300 K, a large number of rotational, torsional, and vibrational energy levels is populated, and this makes for a rather complicated spectrum, which is still not fully understood. It is expected that in going from 300 K to 0.4 K (the temperature of helium nanodroplets) the population distribution of methanol will mainly collapse into two states; the JK = 00 state for the A1 nuclear spin symmetry species (with ICH3 = 3/2), and the JK = 1-1 state for the E species (ICH3 = 1/2). This results in a simplified spectrum that consists of narrow a-type (ΔK = 0) lines and broader b- and c-type (ΔK = ±1) lines. We have recorded the rotovibrational spectrum of CH3OH in the OH stretching, CH3 stretching and bending, CH3 rocking, and CO stretching regions, and have firmly assigned five bands (v1, v2, v3, v7, and v8), and tentatively assigned five others (v9, 2v4, v4 + v10, 2v10, and v4 + v5). To our knowledge, the transitions we have assigned within the v4 + v10, 2v10, and v4 + v5 bands have not yet been assigned in the gas phase, and we hope that considering the very small "matrix" shift in helium nanodroplets (<1 cm(-1) for most subband origins of CH3OH), those made here can aid in their gas phase identification. Microwave-infrared double resonance spectroscopy was used to confirm the initially tentative a-type infrared assignments in the OH stretching (v1) band of A1 species methanol, in addition to revealing "warm" b-type lines. From a rotovibrational analysis, the B rotational constant is found to be reduced quite significantly (56%) with respect to the gas phase, and the torsional tunneling splittings are relatively unaffected and are at most reduced by 16%. While most rovibrational peaks are Lorentzian shaped, and those which are significantly perturbed by vibrational coupling in the gas phase are additionally broadened, the narrowest ΔJ = +1 peaks are asymmetric, and a skew-type analysis suggests that the response time of the helium solvent upon excitation is of the order of 1 ns.

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“…The J = 1 ← 0 pure rotational transition frequency is 20.31(2) GHz in helium nanodroplets as compared to 48.37 GHz in the gas phase. 99 FIG. 4.…”

Section: Oh Stretching Band (V 1 )mentioning

confidence: 96%

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets

Douberly

Jäger

2014

The Journal of Chemical Physics

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“…The rotational spectrum of CD 3 OH was studied already in the early days of microwave spectroscopy in the context of other methanol isotopologs, in particular, in order to determine the molecular structure (Venkateswarlu et al 1955;Nishikawa 1956). Lees & Baker (1968) published the first extensive study of its rotational spectrum in the millimeter wave region by investigating the torsion-rotation interaction in the methanol isotopologs CH 3 OH, CD 3 OH, and CH 3 OD.…”

Section: Introductionmentioning

confidence: 99%

Rotational and rovibrational spectroscopy of CD₃OH with an account of CD₃OH toward IRAS 16293−2422

Ilyushin

Müller

Jørgensen

et al. 2022

A&A

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Solar-type protostars have been shown to harbor highly deuterated complex organics, as evidenced, for instance, by the high relative abundances of doubly and triply deuterated isotopologs. While this degree of deuteration may provide important clues in studying the formation of these species, spectroscopic information on multiply deuterated isotopologs is often insufficient. In particular, searches for triply deuterated methanol, CD3OH, are hampered to a large extent by the lack of intensity information from a spectroscopic model. The aim of the present study is to develop a spectroscopic model of CD3OH in low-lying torsional states that is sufficiently accurate to facilitate further searches for CD3OH in space. We performed a new measurement campaign for CD3OH involving three spectroscopic laboratories that covers the 34 GHz−1.1 THz and the 20−900 cm−1 ranges. The analysis was performed using the torsion-rotation Hamiltonian model based on the rho-axis method. We determined a model that describes the ground and first excited torsional states of CD3OH, up to quantum numbers J ≤ 55 and Ka ≤ 23, and we derived a line list for radio-astronomical observations. The resulting line list is accurate up to at least 1.1 THz and should be sufficient for all types of radio-astronomical searches for this methanol isotopolog. This line list was used to search for CD3OH in data from the Protostellar Interferometric Line Survey of IRAS 16293−2422 using the Atacama Large Millimeter/submillimeter Array. Specifically, CD3OH is securely detected in the data, with a large number of clearly separated and well-reproduced lines. We not only detected lines belonging to the ground torsional state, but also several belonging to the first excited torsional state. The derived column density of CD3OH and abundance relative to the non-deuterated isotopolog confirm the significant enhancement of this multiply deuterated variant. This finding is in line with other observations of multiply deuterated complex organic molecules and may serve as an important constraint on their formation models.

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“…individual residual is that for the b-type 2 0 R 3 1 E 2 transition reported previously (1,2), which must thus be the culprit. This paper has discussed our measurements and assignments for a-type and b-type CD 3 OH millimeter-wave transiOther than the preceding special cases, the small residuals…”

Section: Discussionmentioning

confidence: 98%

“…The final set of 54 adjustable molecular parameters (1)(2)(3)(4)(5)(6). For a more complete picture of the vibration-tor-obtained in this convergent global fit (13) reproduces the sion-rotation energy level structure in CD 3 OH and to im-fitted millimeter transitions to within {100 kHz.…”

Section: Introductionmentioning

confidence: 99%

New Measurements and Assignments in the Millimeter-Wave Spectrum of CD3OH

Predoi‐Cross

Walsh

et al. 1998

Journal of Molecular Spectroscopy

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Methyl Alcohol. I. Microwave Spectrum

Cited by 42 publications

References 3 publications

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets

Rotational and rovibrational spectroscopy of CD₃OH with an account of CD₃OH toward IRAS 16293−2422

New Measurements and Assignments in the Millimeter-Wave Spectrum of CD3OH

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Methyl Alcohol. I. Microwave Spectrum

Cited by 42 publications

References 3 publications

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets

Rotational and rovibrational spectroscopy of CD3OH with an account of CD3OH toward IRAS 16293−2422

New Measurements and Assignments in the Millimeter-Wave Spectrum of CD3OH

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Rotational and rovibrational spectroscopy of CD₃OH with an account of CD₃OH toward IRAS 16293−2422