Prospects for high-resolution microwave spectroscopy of methanol in a Stark-deflected molecular beam (original) (raw)
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Physical Review Letters, 2011
The 6.7 and 12.2 GHz masers, corresponding to the 5 1 ! 6 0 A þ and 2 0 ! 3 À1 E transitions in methanol (CH 3 OH), respectively, are among the brightest radio objects in the sky. We present calculations for the sensitivity of these and other transitions in the ground state of methanol to a variation of the proton-toelectron mass ratio. We show that the sensitivity is greatly enhanced due to a cancellation of energies associated with the hindered internal rotation and the overall rotation of the molecule. We find sensitivities of K ¼ À42 and K ¼ À33, for the 5 1 ! 6 0 A þ and 2 0 ! 3 À1 E transitions, respectively. The sensitivities of other transitions in the different isotopologues of methanol range from À88 to 330. This makes methanol a sensitive probe for spatial and temporal variations of the proton-to-electron mass ratio.
Decelerated molecular beams for high-resolution spectroscopy
The European Physical Journal D, 2004
Ultimately, the resolution of any spectroscopic experiment is limited by the interaction time between the particles that are to be examined and the measuring device. The obtainable spectroscopic resolution in a molecular beam experiment can be considerably improved using samples of slow molecules, as produced, for example, in a Stark-decelerator. This is demonstrated here by measuring the inversion tunneling spectrum of 15 ND3 using a pulsed molecular beam that has been decelerated to about 52 m/s. Hyperfine resolved inversion transitions in 15 ND3 in the |J, K = |1, 1 state (around 1.43 GHz) are induced in a microwave region, and 15 ND3 molecules that have undergone the transition are subsequently detected using a UV-laser based ionization detection scheme. To increase the signal intensity, the decelerated molecular beam is both transversally and longitudinally focused into the laser detection region. The observed spectral width of individual hyperfine transitions in the fully resolved spectrum is about 1 kHz, and the standard deviation of the best fit is 62 Hz.
Millimeter-Wave Spectra and Global Torsion–Rotation Analysis for the CH3OD Isotopomer of Methanol
Journal of Molecular Spectroscopy, 2000
New millimeter-wave and microwave measurements for CH 3 OD have been combined with previous literature data and with an extended body of Fourier transform far-infrared observations in a full global analysis of the first two torsional states (v t ϭ 0 and 1) of the ground vibrational state. The fitted CH 3 OD data set contained 564 microwave and millimeter-wave lines and 4664 far-infrared lines, representing the most recent available information in the quantum number ranges J Յ 20 and K Յ 15. A 53-parameter converged global fit was achieved with an overall weighted standard deviation of 1.060, essentially to within the assigned measurement uncertainties of Ϯ100 kHz for almost all of the microwave and millimeter-wave lines and Ϯ6 MHz for the far-infrared lines. The new parameters for CH 3 OD are compared to previous results obtained for the 12 CH 3 OH, 13 CH 3 OH, and CD 3 OH isotopomers over the same quantum number ranges using the identical fitting program. Strong asymmetry-induced coupling between the accidentally near-degenerate 0E and Ϫ1E v t ϭ 0 substates is successfully modeled by the fit. TABLE 2 CH 3 OD MW and MMW v t ؍ 0 4 0 and v t ؍ 1 4 1 Transitions of A Torsional Symmetry for J < 20,
Microwave and submillimeter-wave rotational spectrum of methyl alcohol in the ground torsional state
Journal of Molecular Spectroscopy, 1992
The frequencies of 440 transitions of the spectrum of the ground torsional-vibrational state of methyl alcohol have been measured in the microwave and submillimeter regions, 130 of these belonging to the main isotopomer CHrOH (J < 42, K < 8), 190 to the isotopomer CDpOH (J =S 37, K 8 IO), and 120 to CDrOD (J < 27, KC 5). For the first time, all the transitions were identified on the basis of directly calculated frequencies. These results were obtained through the use of a new effective torsional-rotational Hamiltonian. Its parameters were calculated based on the frequencies of all earlier known and new transitions of microwave and submillimeter-wave spectra of the ground torsional-vibrational state of methanol The root-mean-square deviation is 710 kHz (800 lines) for the main isotopomer, 144 kHz (370 lines) for CDrOH, and 316 kHz ( 150 lines) for CDSOD.
Methanol is observed in a wide range of astrophysical sources throughout the universe, and comprehensive databases of the millimeter and THz spectra of CH 3 OH and its principal isotopologues represent important tools for the astronomical community. A previous combined analysis of microwave and millimeter wave spectra of 13 CH 3 OH together with Fourier transform far-infrared spectra was limited to the first two torsional states, m t = 0 and 1, for J values up to 20. The limits on frequency and quantum number coverage have recently been extended by new millimeter and THz measurements on several different spectrometers in the Cologne laboratory in the frequency windows 34-70 GHz, 75-120 GHz, 240-340 GHz, 360-450 GHz and 1.12-1.50 THz. With the new data, the global treatment has now been expanded to include the first three torsional states for J values up to 30. The current 13 CH 3 OH data set contains about 2300 microwave, millimeter-wave, sub-millimeter and THz lines and about 17,100 Fourier-transform far-infrared lines, representing the most recent available information in the quantum number ranges J 6 30, K 6 13 and m t 6 2. The transitions have been successfully fitted to within the assigned measurement uncertainties of ±50 kHz for most of the frequency-measured (i.e. MW, MMW, Sub-MMW, THz) lines and ±6 MHz for the FIR lines. A convergent global fit was achieved using 103 adjustable parameters to reach an overall weighted standard deviation of 1.37. Our new C-13 methanol database is improved substantially compared to the existing one , and will be available in the Cologne Database for Molecular Spectroscopy, CDMS (http://www.astro.uni-koeln.de/cdms/), in support of astronomical studies associated with results from HIFI (Heterodyne Instrument for the Far-Infrared) on the Herschel Space Observatory and new observations from SOFIA (Stratospheric Observatory For Infrared Astronomy) and ALMA (Atacama Large Millimeter/Submillimeter Array).
Journal of Molecular Spectroscopy, 2014
We report the design of an experiment that aims to constrain, over a-fewyear timescale, the fractional temporal variation of the proton-to-electron mass ratio, β = m p /m e , at a level of 10 −15 /yr by means of a spectroscopic frequency measurement on a beam of cold CF 3 H molecules. This is extracted from a buffer-gas-cooling source and then collimated by means of an electrostatic hexapole lens. Employed in a two-photon Ramsey-fringes interrogation scheme, the probe source is based on a mid-infrared quantum cascade laser, phase-locked to a specially-developed optical frequency comb that is ultimately referenced to the Cs primary standard via an optical fiber link.
Journal of Molecular Spectroscopy, 1998
A global analysis of reported microwave (MW) millimeter wave (MMW), and Fourier-transform far-infrared (FTFIR) spectra of the CD 3 OH isotopic species of methanol has been carried out for the first two torsional states (n t Å 0 below the barrier and n t Å 1 straddling the barrier) of the ground vibrational state. The CD 3 OH data set contains 472 MW and MMW lines and 5320 FTFIR lines, representing the most recent available information in the quantum number ranges J°20 and K°15. The transitions have been successfully fitted to within the assigned measurement uncertainties of {100 kHz for most of the MW and MMW lines and {6 MHz for the FIR lines with the use of a program (I. Kleiner and M. Godefroid, private communication) based on the formalism of Herbst et al. (J. Mol. Spectrosc. 108, 42-57, 1984). A convergent global fit was achieved using 54 adjustable parameters to reach an overall weighted standard deviation of 0.966. The new parameters for CD 3 OH are compared with previous global fitting results for the 12 CH 3 OH and 13 CH 3 OH isotopomers. ᭧ 1998 Academic Press
Journal of the Optical Society of America B, 1994
High-resolution Fourier-transform spectra of the lower vibrational fundamentals of the 13CD 3 OH isotopomer of methanol are under investigation in the 800-1350-cm-1 region, including the vs in-plane CD 3 -rocking (A'), V7 CO-stretching (A'), V5 CD 3 -deformation (A'), and V4 OH-bending (A') bands. The torsion-vibration-rotation energy-level manifold for these lower modes displays numerous perturbations that are due to torsion-vibration interactions and contains a variety of features of interest in the excited-state energy-level patterns. Analyses of the bands show that there are major problems in formulating effective Hamiltonians and in determining reliable molecular constants for the excited states because of strong torsion-vibration coupling. Assignments for five far-infrared laser transition systems have been deduced; these involve the CD 3 -rocking, CO-stretching, and CD 3 -deformation states.
Chemical Physics Letters, 2014
Fragmentation and isomerization of methanol cation by short, intense laser pulses were studied by ab initio classical trajectory simulations using CAM-B3LYP/6-31G(d,p) calculations. Compared to random orientation, CH 3 OH + with the C O bond aligned with the laser polarization gained nearly twice as much energy from the laser field, in accordance with the higher vibrational intensities in the mid-IR range for aligned CH 3 OH +. The energy gained by CH 3 OH + from 7 m and 800 nm laser pulses with intensities of 0.88 × 10 14 and 1.7 × 10 14 W/cm 2 is proportional to the intensity and the wavelength squared of the laser field.