Laser stark spectroscopy of13CH3F

The far-infrared laser Stark spectrum of¹³CH₃F has been observed using the 190 m line of the DCN laser. The spectrum was taken at room temperature for both parallel and perpendicular polarizations up to 60,000V/cm. We identify the transition as J_k=32₁₄31₁₄ in the ground vibrational state. The measured zero-field frequency for this transition is in agreement with that calculated from the available molecular constants.     

Far-infrared laser stark spectroscopy of CH3OH and13CH3OH

The high resolution laser Stark spectra of methanol and¹³C-substituted methanol have been studied up to Stark fields of about 60 000V/cm with the HCN and DCN lasers. Numerous families of absorption lines have been observed in both parallel and perpendicular polarizations. For methanol, the transitions J _k =7₅ 6₄ A, _t=0; J _k =11₄ 10₃ E _l , _t=0; and J _k =17₃ 16₂ E₂, _t=0 have been identified while the assignments for¹³C-substituted methanol are J _k =14₈ 15₇ A, _t=0; J _k =15₃ 14₂ A⁺, _t=0; J _k =10₇ 9₆ A, _t=0; and J _k =27₉ 27₈ E₁, _t=0. Zero-field frequencies for the assigned transitions are given with improved accuracy over those calculated from available molecular constants, especially for¹³CH₃OH.     

13CH3OH and13CD3OH optically pumped fir laser: New large offset emission and optoacoustic spectroscopy

27 new, large offset, FIR laser lines from¹³CH₃OH and one from¹³CD₃OH have been discovered by pumping with a high tunability waveguide CW CO₂ laser. Optoacoustic measurements of isotopic methyl alcohol have also been performed and the pump offsets of the new and of previously known lines have been measured and checked. Frequency tunability by Stark effect has been observed for 6 strong lines. Some assignments are discussed.     

Frequency measurements of 3 to 11 THz laser lines of CH3OH

We measured the frequencies of 12 far-infrared laser lines generated in a high- frequency Fabry-Perot laser cavity containing methanol, pumped by a CO₂ laser. The frequencies are in the range 2.8 to 11.4 THz (105.4 to 26.2 µm). Ten of the measured frequencies are higher than 7 THz, and help to fill the laser frequency gaps in this region. Five of the measured lines are new. The 11.4 THz line has the highest frequency of an optically pumped laser ever measured with the CO₂ laser heterodyne technique.This work has been financed by the Brazilian Government - Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and by the United States Government - NASA Grant W-18, 623.Contribution of NIST, not subject to U.S. Copyright.     

Acoustooptic extension of the frequency tunability of CW CO2 lasers: New FIR lasers emissions from CH3OH and13CH3OH

We have increased the frequency tunability of our CW waveguide CO₂ lasers by means of an acoustooptic amplitude modulator, operating at the fixed frequency of 90 MHz. The up-shifted, or down-shifted, laser optical sideband can be generated independently by adjusting the orientation of the modulator. The efficiency is larger than 50%. The frequency tunability of the CO₂ laser around each laser line is thus increased by 180 MHz. To demonstrate the possibilities of this method, a source composed of the above modulator and of a CW, 300 MHz tunable waveguide CO₂ laser has been used for the search of new large offset FIR laser lines from optically pumped CH₃OH and¹³CH₃OH molecules. As a result 15 and 10 new large offset laser lines were discovered respectively. New assignments of some laser lines are also proposed. We have also measured the Stark effect, the offset, and the polarization of other already known lines. In particular a Stark effect frequency tuning of about 1 GHz is demonstrated for a laser line at 208.399 m.     

Far infrared laser lines and assignments of CH3OH: a review

Methyl alcohol is the most important lasing molecule in the Far-Infrared (FIR) spectral region, and the most widely used for investigation and for applications. Since the last critical review of 1984, over seventy papers have been published dealing with the FIR laser lines and the infrared spectroscopy of CH₃OH. In 1984 we could list about 330 FIR laser lines, 98 of which were measured in frequency and 105 assigned. Since then more than 70 papers were published increasing the number of the known laser lines to 575 (103 measured in frequency). Also the FIR and IR spectroscopy was largely improved thanks to the analysis of high resolution FT spectra, and the number of the correctly assigned laser lines has been increased to 224. The wavenumbers of the assigned lines can now be predicted with an accuracy of about 0.001 cm^–1 or better, thus approaching the accuracy of the experimental frequency measurements.     

Infrared and far-infrared spectroscopy of CH3OH: TeraHertz laser lines and assignments

We use a ¹³CO₂ laser as optical pumping source to search for new THz laser lines generated from ¹³CH₃OH. Nineteen new THz laser lines (also identified as far-infrared, FIR) ranging from 42.3 μm (7.1 THz) to 717.7 μm (0.42 THz) are reported. They are characterized in wavelength, offset, relative polarization, relative intensity, and optimum working pressure. We have assigned eight laser lines to specific rotational energy levels in the excited state associated with the C-O stretching mode.     

Far-infrared spectrum of excited torsional states of C-13 methanol

The torsion-rotation structure of the far-infrared (FIR) spectrum of the C-13 isotopic species of methyl alcohol has been investigated by high-resolution Fourier transform spectroscopy in the 25–350 cm^–1 region, with emphasis on subbands involving excited torsional states. In this study, 89 such subbands have been identified, with torsional states fromn=1 ton=3 included. As well, a further 4 assignments have been added to our previous work on then=0 ground torsional state. The subband origins together with known microwave results have been fitted by least-squares to our torsion-rotation Hamiltonian, and improved molecular structural and torsional constants for the vibrational ground state are reported. Tables of state-specific constants representing the three leading terms in aJ(J+1) power-series expansion of the torsion-rotation energy levels are given for torsional statesn=0 to 3 and rotationalK values from 0 to 16.     

IR and FIR Spectroscopy of 13CH3I

We have investigated the ¹³CH₃I isotopomer of methyl iodide as a source of Far Infrared (FIR) laser radiation using the optical pumping technique. The molecule is pumped by using a pulsed waveguided CO₂ laser, driven by a novel all solid state power supply that lases on the 10HP band as well as the regular bands. We discovered and assigned two new FIR laser emissions and we give further spectroscopic information about polarization and pump frequency offset for five already known lines.