Far-infrared Laser Lines Research Articles

Very high-resolution Synchrotron radiation far infrared spectrum of C-13 methanol arising from the ground torsional vibrational state and evidence of avoided crossing due to ΔK = 4 interaction

In this work, very high-resolution far-infrared (FIR) and infrared (IR) Synchrotron Radiation spectra of C-13 substituted methanol species have been recorded with very high signal-to-noise (S/N) ratio in the entire region from 40 to 5000 cm−1. High resolution allowed the recording to be done with an unprecedented resolution of about 0.0014 cm−1 which is on the order of the doppler width of the lines. The peak of the spectral lines could be obtained with an estimated accuracy of ± 5 KHz. Analysis of the spectra has been performed for quantum numbers associated with the torsional ground state. Assignments have been obtained for K- values up to about 15 and J- values of about 35 for the three symmetry species. Asymmetry splitting has been observed for low K transitions and accurate asymmetry splitting constants have been obtained. Including the available microwave (MW) and millimeter-wave (MMW) measurements, a complete set of spectral line assignments have been obtained for the ground torsional state of the vibrational state. Following J.K. Watson’s method [1] all the spectral lines have been fitted to the exact term values of the energy levels. Localized perturbation has been observed for K = 9 A and state mixing resulted in forbidden transitions through intensity borrowing. A complete atlas has been presented for all possible quantum numbers for the ground state levels and the accurate term values have been obtained for all possible states. According to our knowledge, this atlas represents the most accurate line positions for this species reported so far. In addition, the results have been applied to confirm and obtain very accurate wavenumbers for several FIR laser lines pumped by CO2 lasers. The present atlas may be useful as a secondary wavenumber standard in the FIR region and should be useful for astrophysical detection.

Very high-resolution synchrotron radiation far-infrared (FIR) spectrum of methanol‑D2 (CHD2OH) & millimeter-wave (MMW) measurements involving highly excited torsional vibrational rotational states, and identification of optically pumped FIR laser lines

Synchrotron radiation-based very high-resolution far-infrared (FIR) spectrum recorded at the Canadian Light Source (CSL) of doubly deuterated asymmetric methanol molecule (CHD2OH) have been analyzed for transitions associated with highly excited torsional-vibration–rotation levels. Complimentary millimeter-wave (MMW) transition frequencies have been measured using a backward wave oscillator based spectrometer at the Ohio State University. A new and simplified model has been proposed to treat the Hamiltonian Eigenvalues which do not require a large number of parameters with uncertain physical significance. A systematic approach has been laid out on how to proceed in order to obtain self-consistent and rigorously confirmed assignment of an extremely complicated spectrum arising due interaction with other states. New measurements in the MMW region should facilitate astrophysical determination of column densities of this abundant molecular species in cold interstellar clouds, especially in star-forming regions. The scarcity of MMW and the FIR laboratory database severely hindered the astrophysical work in the past. All the FIR assignments have been rigorously confirmed by closed combination relations (CR) using the MMW measurements and/or through ground state CRs from fundamental vibrational band analysis. These FIR transitions are presented in the form an atlas of about 900 lines. As a byproduct of the measurements, it was possible to put forward tentative assignments of optically pumped FIR laser lines.

Lamb-dip spectroscopy of the C-N stretching band of methylamine by using frequency-tunable microwave sidebands of CO2 laser lines.

Lamb-dip spectroscopy of the C−N stretching band of methylamine has been systematically extended to P-, Q-, and R-branch by using microwave sidebands of a large number of CO2 laser lines as frequency-tunable infrared sources in a sub-Doppler spectrometer. Lamb-dip signals of more than 150 spectral lines have been observed with a resolution of 0.4 MHz and their frequencies have been precisely measured with an accuracy of ±0.1 MHz. More than 30 closed combination loops have been formed, which unambiguously confirm the assignments. For over 150 vibrational excited levels in 27 substates, refined term values have been determined and expanded in J(J + 1) power-series to determine the substate origins and the effective rotational constants. For transitions with Aa torsion-inversion symmetry in torsional state υt = 0, 57 K-doublet lines displaying asymmetry splittings have been observed and the splitting constants for levels with K = 1, 2, and 3 in the excited states have been determined. Our results provide accurate experimental information for spectroscopic studies of the interesting vibrational perturbations and intermode interactions related to the C−N stretching mode, directly support astronomical surveys, and are very relevant in practice to identification and frequency determination of the CO2-laser-pumped far-infrared laser lines of methylamine.

High resolution infrared spectrum of the CD2 wagging band of methanol-D2 (CHD2OH) for the lowest lying torsional vibrational state (e0)

This paper reports the analysis of the high resolution (0.0019cm−1) Fourier transform infrared (FTIR) spectrum for asymmetrically deuterated methanol CHD2OH (methanol-D2) at a low temperature for the CD2 wagging band for the lowest lying trans-species (e0). In spite of the complexity and perturbation in the spectra, assignments were possible for the CD2 wagging band for a maximum K value of 10. In total, about 500 spectral lines have been assigned. Analysis of the spectral lines has been performed in terms of state dependent molecular parameters, Q-branch origins and asymmetry splitting. Assignments have been thoroughly confirmed using combination relations (see text). The catalogue of the assigned transition wavenumbers will help identification and prediction of far infrared (FIR) optically pumped CO2 lasers. The absorption lines close to the several 10R and 10P CO2 laser lines have also been identified. These should help experimentalists to optimize the power of the emission FIR laser lines and to predict new lines and should prove valuable as a laboratory support for interstellar detection in “Radio Astronomy”. To our knowledge this is the first time such vibrational infrared (IR) high resolution study in CHD2OH is being performed.

Far infrared spectrum of Methanol-D2 in the lowest torsional state (e0)

The infrared (IR) and far infrared (FIR) absorption spectra have been measured for the Methanol-D1 and D2 species in the wave number range of 20–1200cm−1 at the Justus Liebig Universität in Giessen, Germany using a Brüker Fourier Transform spectrometer at a resolution of 0.002cm−1. The spectra looked very complicated but analyses were possible for the lower lying states. At higher wave number regions spectra of few vibrational fundamental modes were visible. In this communication, the details of the assignments and analyses of the lowest lying internal rotational state (e0) for Methanol-D2 are reported. A catalog of about 900 assigned spectral lines has been prepared and is made available from the author to conserve space. As application of this work, it was possible to assign some optically pumped FIR laser lines to quantum states. The results should be useful for “radio astronomers” and in the field of optically pumped FIR and Sub-millimeter Wave (SMMW) lasers which are used in Tokamaks for plasma diagnostics and as local oscillators in radio detection from space.

Fourier Transform Infrared spectrum of the OCD bending mode in methanol-D1

The infrared (IR) spectra corresponding to OCD bending vibration of asymmetrically deuterated methanol species CH2DOH have been recorded with a Fourier Transform Spectrometer. The spectrum shows a typical structure of a parallel a-type band. This is expected because the bending vibration mainly executed parallel to the symmetry axis The Q-branch lines are grouped closely around 896cm−1 and the P- and R-Branches show complex structure. Nonetheless it was possible to assign a-type P- and R-branch lines up to K value of 8 and J value up to about 20 in most cases. The Q-branch lines for higher K values can be followed to about J=15, the presence of which confirmed the assignments. The observations suggest that in the OCD bend some energy levels are highly interacted by highly excited torsional state from the ground torsional state. A full catalogue is presented along with the effective molecular parameters. An intensity anomaly was also observed in the transitions. So far it has been possible to assign only transitions between e0←e0 states. Plausible explanations of intensity anomaly are presented. Lastly, a number of optically pumped far infrared (FIR) laser lines have been assigned either to exact or tentative quantum states. These assignments should prove valuable for production of new FIR laser lines.

Assignment of far-infrared laser lines of O-17 methanol by synchrotron FTIR spectroscopy and laser frequency measurements

Analysis of synchrotron FTIR spectra has revealed new assignments for a number of optically pumped far-infrared laser lines from the CH317OH isotopologue of methanol, with definitive confirmation provided by recent accurate measurements of the laser frequencies. In this Note the lasing energy level systems are discussed, and the spectroscopic evidence for the assignments is presented.

New cw Optically Pumped Far-Infrared Laser Emissions Generated with a Transverse or ‘Zig-Zag’ Pumping Geometry

This work reports the observation of several novel far-infrared laser lines obtained through optical pumping of a gaseous medium using a transverse or zig-zag excitation scheme. In total, about 160 laser emissions with wavelengths up to 1.1 mm have been observed. This includes nine new laser lines detected from CH3OD, CH2 F2, and CD3 I which are reported with their operating pressure, relative power, and wavelengths measured to ± 0.5 μm.

High-Resolution Frequency Measurements of Far-Infrared Laser Lines

The frequency of four previously reported far-infrared laser lines have been measured to an accuracy of 100 kHz. These laser lines were measured using a heterodyne system which allowed for more accurate measurement. The four far-infrared laser lines which originated from Formic Acid (HCOOH), O-Deutero-Formic Acid (HCOOD), C-Deutero-Formic Acid (DCOOH), and Methyl Chloride (CH3Cl) were optically pumped by a highly stable, grating-tunable, CO2 laser. Three of the far-infrared laser lines have been measured previously using Fabry-Perot cavities not typicaly known for their high accuracy. The fourth far-infrared laser line had been measured previously by heterodyne methods but under nonoptimal conditions. The difference between the frequencies measured here and the listed frequencies for these laser lines ranged from 0.9 MHz to 3.9 GHz.

New Terahertz Laser Lines From $^{13}{\hbox {CD}}_{3}{\hbox {OH}}$ Pumped by Regular and Hot Bands ${\hbox {CO}}_{2}$ Laser

We have used our new pulsed CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser, operating both on regular and hot bands, to excite the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> CD <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> OH methanol isotopomer. This has lead to the observation of 13 new high-threshold far-infrared laser emissions (also identified as terahertz laser lines), with frequencies in the range between 24.11 and 102.56 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> (0.72-3.07 THz). The absorption transitions leading to these new FIR laser emissions have been located by observing the optoacoustic absorption spectra around the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> emissions. Here, we present these new far-infrared laser lines, characterized in wavelength, polarization, offset relative to the center of the pumping CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser transition, relative intensity, and optimum operation pressure.

Far-Infrared Laser Assignments for Methylamine

Reported far-infrared laser lines for five different transition systems of CH3NH2 optically pumped by a CO2 laser have been identified spectroscopically through a high-resolution Fourier transform infrared study of the C-N stretching band together with CO2-laser/microwave-sideband broad-scan and Lamb-dip measurements. From the infrared analysis plus previous far-infrared (FIR) results for the ground vibrational state, quantum numbers have been assigned for seven methylamine FIR laser transitions and their C-N stretching pump absorptions coincident with the CO2 laser lines. The assignments are confirmed through the use of closed frequency combination loops that also provide improved FIR laser frequencies to spectroscopic accuracy.

Spectroscopic study of the 14NH radical in vibrationally excited levels of the X3Σ− state by far infrared laser magnetic resonance

Rotational transitions of vibrationally excited NH (ν = 1 and 2) in the ground X3Σ− electronic state have been detected by far-infrared laser magnetic resonance. The first four rotational intervals were investigated (N = 1 − 0, 2 − 1, 3 − 2, and 4 − 3) with a total of 17 far-infrared laser lines ranging in wavelength from 81.1 to 373.6 µm. For some rotational intervals, transitions between all components of the Zeeman manifolds were observed. An effective Hamiltonian was used to model the experimental measurements. The magnetic hyperfine parameters have been determined for the first time for the ν = 2 level and have been significantly improved for the ν = 1 level. In addition, the rotational, centrifugal distortion, spin-spin, spin-rotation, and Zeeman parameters have all been experimentally determined for the ν = 1 and 2 levels of NH.

CH3OH optically pumped by a 13CO2 laser: new laser lines and assignments

We report 12 new THz (far-infrared) laser lines from methanol (CH3OH), ranging from 58.1 μm (5.2 THz) to 624.6 μm (0.5 THz). A 13CO2 laser of wide tunability (110 MHz) has been used for optical pumping, allowing access to previously unexplored spectral regions. Optoacoustic absorption spectra were used as a guide to search for new THz laser lines, which have been characterized in wavelength, polarization, offset, relative intensity, and optimum operation pressure. For 20 laser lines previously observed, we have measured the absorption offset with respect to the 13CO2 laser line center.

12CH3OH and 13CH3OH optically pumped by the 10P and 10HP bands of a pulsed CO2 laser: New far-infrared laser emissions and assignments

We have re-investigated the 12CH3OH and the 13CH3OH molecules as optically pumped far-infrared laser sources. We have used our new waveguide pulsed-high-peak-power CO2 laser for pumping, finding 20 new far-infrared laser lines emitted by 12CH3OH and seven emitted by 13CH3OH. For each line we report wavelength, pump offset from the center of the exciting CO2 line, relative polarization, optimum operating pressure and intensity. The LaseRitz program was able to assign one of the new laser systems of 12CH3OH, involving two new far-infrared laser lines.

Hydrazine far-infrared laser lines and assignments: a review

The hydrazine molecule is one of the most prolific far-infrared (FIR) laser sources. We present a complete list of its 268 observed FIR laser emissions excited by the ^12 C ^16 O2 laser. For each line we report all the available data on the CO2 pump line, the frequency measurement when available, the wavelength, the optimum operating pressure, the relative intensity, the polarization relative to the pump radiation, and the absorption offset from the CO2 line center. In spite of the large amount of experimental research performed on the hydrazine laser, only a few papers have reported the assignments of the levels involved in the laser systems. In fact, a systematic assignment of the IR hydrazine absorption spectrum is only at a preliminary stage owing to the complexity of the Hamiltonian of this molecule. We have investigated the possible assignments for all the reviewed FIR laser emissions by comparison with an N2H4 absorption spectrum. We can confirm the assignments for only 37 FIR laser lines belonging to 20 laser systems.

Characterization of new FIR laser lines from CHD/sub 2/OH

In this work, we report new optically pumped far-infrared (FIR) laser lines from CHD/sub 2/OH. A waveguide CO/sub 2/ laser of wide tunability (290 MHz) was used as pump source, and a Fabry-Pe/spl acute/rot open cavity was used as a FIR laser resonator. Optoacoustic absorption spectra were used as a guide to search for new FIR laser lines. We could observe 15 new laser lines in the range from 116.4 to 401.4 /spl mu/m. The lines were characterized according to wavelength, relative polarization, relative intensity, and optimum working pressure. The transferred Lamb-dip technique was used to measure the frequency absorption transition both for the new and previously reported laser lines.

Re-investigation of optically pumped hydrazine far-infrared laser around 11 /spl mu/m from the 10HP and 10P bands of a pulsed CO/sub 2/ laser: new lines and assignments

A high-peak-power (several hundreds of watts) pulsed CO/sub 2/ laser, recently developed in our laboratory, has been used for exciting optically pumped far-infrared laser transitions of N/sub 2/H/sub 4/. A systematic search for N/sub 2/H/sub 4/ absorption coincidences with 10P and 10HP CO/sub 2/ laser emissions has led to the observation of 27 new far-infrared laser lines, excited by 18 different absorption transitions. All of these new lines have been characterized in wavelength, offset, relative polarization, optimum operation pressure and intensity. Using the LaseRitz program, ten of these lines were assigned, corresponding to five laser systems. For other two laser systems possible J and K quantum numbers of the energy levels involved in the laser transitions were given.

New far-infrared laser lines from CH/sub 3/OD methanol deuterated isotope

We report on a study of the CH/sub 3/OD molecule in a search for new far-infrared (FIR) laser lines. For optical pumping of large offset vibrational absorption transitions, a continuous-wave waveguide CO/sub 2/ laser with 300 MHz tunability around each line was used for the first time. As a consequence, 17 new far-infrared laser emissions were observed. For these lines, we also present data on wavelength, intensity, offset, relative polarization, and optimum operation pressure.

FIR Laser Lines from CH3OD: A Review

The methanol isotopic species CH3OD has also proved to be an efficient and powerful medium to generate radiation in the far infrared (FIR) region. After the critical review of 1994, six papers have been published dealing with new FIR laser lines from this molecule. As a consequence of the use of wide tunability waveguide CO2 lasers as well as a new pulsed CO2 laser operating at hot and sequential bands, as of optical pumping sources, the total number of the FIR laser lines increased from 122 in 1994 to 227 today. In this communication we present an updated and complete catalogue of FIR laser lines generated from CH3OD. Information on wavelength, offset, relative polarization, intensity, and optimum operation pressure is generally available.

New FIR laser lines from hydrazine and assignments

Our new waveguide pulsed CO2 laser, with peak powers above 1 kW, has allowed us to observe 24 new far-infrared laser lines emitted by hydrazine. Each of them is characterized in wavelength, relative polarization, intensity, optimum operating pressure and pump offset from the center of the exciting CO2 line. These new laser emissions either form pairs sharing the same pump line, or complete such pairs with lines known from the literature. In the latter case, we have measured the relative polarization and offset of the partner lines whenever they were not reported in the literature. The availability of laser systems with two emission lines orthogonally polarized and sharing the same upper level is expected to facilitate the assignment work. We present complete assignments for four FIR laser emissions, and we propose J and K values for 12 further laser systems.