Sub-millimeter wave spectroscopy of CHD2OH: a-type and asymmetry induced c-type transitions in the lowest three torsional sub-levels

The sub-millimeter wave (SMMW) spectral measurements using a fast scan backward wave oscillator based spectrometer have been carried out for asymmetrically deuterated methanol CHD₂OH (Methanol-D₂). Transition frequencies have an estimated uncertainty of about ±50 kHz. Albeit the complexity in the spectra, assignments were possible for a large number of a-type (ΔK = 0) transitions. In the course of the assignment process a strong c-type (ΔK = 1) Q-branch connecting two states of different symmetry species has been identified. This Q-branch assignment is significant because it is forbidden in the normal parent species CH₃OH. It becomes allowed in the current species due to the effects of the asymmetry introduced by the off-axis deuterium in the hindering potential to the internal rotation in the molecule. The assignments are rigorously confirmed using combination relations which required the measurement of some other related lines. To our knowledge this is the first time such symmetry breaking transitions are reported in CHD₂OH and in fact this is the first time the SMMW spectrum of CHD₂OH is being reported. Detailed spectral study of this molecule in the IR and FIR regions is in progress and will be reported elsewhere. Detailed study of the identification optically pumped FIR laser line is underway.     

Discovery and frequency measurement of short-wavelength far-infrared laser emissions from optically pumped <Superscript>13</Superscript>CD<Subscript>3</Subscript>OH and CHD<Subscript>2</Subscript>OH

A three-laser heterodyne system was used to measure the frequencies of twelve previously observed far-infrared laser emissions from the partially deuterated methanol isotopologues ¹³CD₃OH and CHD₂OH. Two laser emissions, a 53.773 μm line from ¹³CD₃OH and a 74.939 μm line from CHD₂OH, have also been discovered and frequency measured. The CO₂ pump laser offset frequency was measured with respect to its center frequency for twenty-four FIR laser emissions from CH₃OH, ¹³CD₃OH and CHD₂OH. PACS 07.57.Hm; 42.55.Lt; 42.62.Eh     

A review of optically pumped far-infrared laser lines from methanol isotopes

The technique of optical pumping in polar molecules is the most efficient for Far-Infrared (FIR) laser generation, providing also a versatile and powerful tool for molecular spectroscopy in this spectral region. Methanol (CH₃OH) and its isotopic varieties are the best media for optically pumped FIR laser, with over thousand lines observed, and the most widely used for investigations and applications. In this sense, it is important organize and make available catalogues of FIR laser lines as complete as possible. Since the last critical reviews of 1984 [1] on methanol and its isotopic varieties [2,3,4], over hundred papers have been published dealing with hundreds of new FIR laser lines. In 1992 a review of FIR laser lines from CH₃OH was presented [5]. In this communication we extend this work to the other methanol isotopes, namely CH₃OD, CD₃OH, CD₃OD,¹³CH₃OH,¹³CD₃OH,¹³CD₃OD, CH₃ ¹⁸OH, CH₂DOH, CHD₂OH and CH₂DOD.Work supported by FAPESP, CNPq, FAEP-Brasil, and CNR-Italia     

IR and FIR spectroscopy of 13CD3OH around the 10P(22) and 10P(24) CO2 laser lines: New FIR laser emissions,frequency measurements and assignments

By using high resolution infrared Fourier transform data on ¹³CD₃OH and the 10P(22) and 10P(24) lines of a waveguide CO₂ laser to optically pump this methanol isotope, eight new FIR laser lines were observed. The frequencies of five laser lines were directly measured by heterodyne detection with already known laser lines. Particularly interesting are the lines pumped by the 10P(24) line, since a triade of emissions could be completely assigned.     

Spectroscopy of the excited C-O stretching Q branch of 13CD3OH: Measurement and assignment of new FIR laser lines

The Q branch of the C-O stretching fundamental band of ¹³CD₃OH has been investigated. Starting from a high resolution (4 × 10⁻³cm⁻¹) infrared Fourier transform spectrum and using a waveguide CO₂ laser of 300 MHz tunability and an acoustooptic modulator for an extension of ±90 MHz, 31 new FIR laser lines have been observed. The related absorptions have been measured by means of optoacoustic detection. The frequency of one new FIR laser line was also measured. Eight tentative assignments are proposed for the IR absorption and FIR laser emissions.     

High-resolution FTIR spectroscopy of CHD279Br: ro-vibrational analysis of the v4 fundamental and determination of the ground state constants

The first high-resolution infrared spectrum of CHD₂⁷⁹Br has been investigated by Fourier transform spectroscopy in the range 940–1100 cm^?1 at an unapodised resolution of 0.0025 cm^?1. This spectral region is characterised by the v₄ (1036.8389 cm^?1) fundamental band, corresponding to the CD₂ wagging mode. The rotational structure of the a- and c-type components of the hybrid band has been extensively assigned for transitions involving values of J and K_a up to 65 and 15, respectively. The ground state constants up to the quartic centrifugal distortion terms have been obtained for the first time by ground state combination differences from 5251 assigned transitions and subsequently employed for the evaluation of the band origin and the excited state parameters of v₄. Watson’s S-reduced Hamiltonian in the I^r representation has been used in the ro-vibrational analysis. The dipole moment ratio |Δμ_a/Δμ_c| of the band has been estimated to be 1.3?±?0.1 from spectral simulations.     

New laser lines from CHD2OH methanol deuterated isotope

Through the optical pump technique we have reinvestigated the CHD₂OH molecule as a source of far-infrared (FIR) laser lines using for the first time a CO₂ laser lasing on regular, hot, and sequence bands. As a consequence, we present here spectroscopic data of 16 new FIR laser transitions from this molecule. Furthermore, we also present a catalogue of all FIR laser lines generated from CHD₂OH. Received: 13 July 2001 / Revised version: 25 October 2001 / Published online: 14 May 2002     

Far infrared laser lines produced by methanol and its isotopic species: A review

Methanol (CH₃OH) is considered today one of the most important active media for the generation of laser radiation in the far-infrared (FIR) spectral region. Together with ten of its other isotopic species, it is responsible for the major part of the laser lines generated by the optical pumping technique. Due to the extreme importance of those molecules as laser generators, we understood that there was a necessity of a comprehensive work which would include as much pratical information as possible about each line.Chang et al⁽¹⁾ early recognized methanol as a source of strong FIR laser lines. Since then, more than 100 papers were published containing information about new laser emission. Recently, Moruzzi et al⁽¹¹⁴⁾ presented a review of 575 lines produced by¹²CH₃OH. In the present paper, we have extended the review to the various isotopic modifications of this molecule (namely¹³CH₃OH, CD₃OH,¹³CD₃OH, CD₃OD,¹³CD₃OD, CH₃OD, CH ₃ ¹⁸ OH, CH₂DOH, CH₂DOD and CHD₂OH), a total of nearly 2000 lines with wavelengths ranging from 19µm to 3030µm.     

Very high resolution far infrared synchrotron radiation spectrum of methanol-D1 (CH2DOH) in the first three torsional-vibrational modes

In our effort to systematically study the far infrared (FIR) spectra of asymmetrically mono deuterated methanol (CH₂DOH) and thereby obtain the transition wavenumbers with better and better accuracy (Mukhopadhyay, 2016a,b), the complete Fourier transform (FT) spectra from FIR to infrared (IR) vibrational bands (in the range 50–1190 cm⁻¹) have been re-recorded using the Synchrotron Radiation Source at the Canadian Light Sources in Saskatchewan, Canada. The resolution of the spectrum is unprecedented, reaching beyond the Doppler limited resolution as low as about 0.0008 cm⁻¹ with a signal to noise (S/N) ratio is many fold better than that can be obtained by commercially available FT spectrometer using thermal sources (e.g., Globar). Spectra were also recorded beyond 1190 cm⁻¹ to about 5000 cm⁻¹ at a somewhat lower resolution of 0.002–0.004 cm⁻¹. In this report the analysis of the b-type and c-type torsional - rotational spectra in the ground vibrational state corresponding to gauche- (e₁/o₁) to gauche- (e₁/o₁) and gauche- (e₁/o₁) to trans- (e₀) states in the ground vibrational state are reported and an atlas of the wavenumber for about 2500 FIR assigned absorption lines has been prepared. The transitions within a given sub-band are analyzed using state dependent expansion parameters and the Q-branch origins. The data from previous results (Mukhopadhyay, 2016a,b) along with the present work allowed a global analysis yielding a complete set of molecular parameters. The state dependent molecular parameters reproduce the experimental wavenumbers within experimental uncertainty. In addition, the sensitivity of the spectrum allowed observation of forbidden transitions previously unobserved and helped reassignment of rotational angular momentum quantum numbers of some ΔK = ±1, Q-branch transitions in highly excited states recently reported in the literature. To our knowledge the wavenumbers reported in the present work are the most accurate so far reported in the literature and represent the highest resolution spectra for this molecular species.     

Observation of exciton surface polaritons at room temperature

10 new cw far infrared laser lines have been observed by optically pumping the CD₃ deformation vibration band of CD₃OH with 9 μm CO₂-laser lines     

13CD3OH and12CD3OH optically pumped by a13CO2 laser: Observations and assignments of FIR laser lines

In this work we report the first observation of FIR laser lines from¹³CD₃OH pumped by the¹³CO₂ isotope laser. Using the same pump we have also found 3 new lines from¹²CD₃OH. Tentative assignments for the absorption and emission transitions of the observed lines are also proposed.Work supported by FAPESP. CNPq, FAEP/UNICAMP-Brasil and NSF-USA     

Assignments of optically pumped CD3OH laser lines

Six FIR laser lines from CD₃OH pumped by the 10R(36) and the 10R(18) CO₂ laser lines are assigned to specific rotational energy levels in the excited C–0 stretch state. It is found that their upper laser levels are shifted by a Fermi resonance between the C–0 stretch vibration and the third and forth harmonics of the torsional mode. The Fermi resonance shifts are +0.332 cm^–1 and +2.251 cm^–1 for the upper laser levels pumped by the 10R(36) and the 10R(18) CO₂ laser lines, respectively. Calculated frequencies of the pump and the laser transitions agree with those of the pump CO₂ laser lines and the observed FIR laser lines within estimated accuracy.     

Methylene bromide chemistry and photochemistry on rutile TiO2(110)

The chemistry and photochemistry of methylene bromide (CD₂Br₂) on the rutile TiO₂(110) surface was probed using temperature programmed desorption (TPD). CD₂Br₂ desorbed in three desorption states at 145, 160 and 250 K tentatively assigned to desorption from the multilayer, from an η¹-CD₂Br₂ species and a bridging η²-CD₂Br₂ species, respectively. The latter two TPD states presumably involve binding of CD₂Br₂ molecules to the surface through Br coordination at five-coordinate Ti⁴⁺ surface sites. The 160 and 250 K TPD states saturated at coverages of 1.0 and 0.33 ML, respectively, where 1 ML is equivalent to the surface Ti⁴⁺ site density (5.2 × 10¹⁴ cm^? 2). No thermal decomposition of CD₂Br₂ was observed on either the clean surface or with preadsorbed O₂. UV irradiation of CD₂Br₂ on TiO₂(110) resulted in predominately photodesorption, with trace amounts of photodecomposition evidenced in TPD. The rate of CD₂Br₂ photodesorption from TiO₂(110) occurred with a low cross section (~ 2 × 10^? 21 cm²) similar to that expected from direct optical excitation of CD₂Br₂. This observation suggests that charge carriers generated in TiO₂(110) were no more effective in activating adsorbed CD₂Br₂ molecules than would be expected through direct molecular excitation. These findings suggest that photocatalytic destruction of halocarbons such as CD₂Br₂ on TiO₂ may preferentially occur though indirect processes (such as OH radical attack) as opposed to direct electron transfer processes involving charge carriers generated in TiO₂ by bandgap excitation.     

New fir laser lines and frequency measurements from optically pumped13CD3OH3

We report the discovery of 57 new fir laser lines from¹³CD₃OH molecule optically pumped by a waveguide CO₂ laser of 300 MHz tunability. For all lines, precise frequency offset measurements between the CO₂ line center and the center of the absorbing¹³CD₃OH line were performed using the transferred Lamb-Dip technique. We have also measured directly the frequency of seven FIR laser lines by heterodyning with already known laser lines. We present a complete list of all known laser lines (134) and frequency measurements (24) for this molecule.Work supported by CNPq, FAPESP, FAEP-Brasil, and CNR-Italia     

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.     

Submillimeter laser action of CW optically pumped CF2Cl2 (Fluorocarbon 12)

Eleven new CW far infrared (FIR) laser lines have been observed in the 600 m–1200 m range from the CF₂Cl₂ (Fluorocarbon 12) molecule optically pumped by a CO₂ laser. A 510^–4–10^–3 accuracy is achieved in the measurement of the FIR wavelengths.The frequency offset between the CO₂ pump center and the absorption line centers are measured using the transferred Lamb dip technique. Owing to a recent spectroscopic study of the CF₂ ³⁵Cl₂ molecule three lines may be assigned with great confidence as rotational transitions in thev ₆ vibrational band 923 cm^–1 of this main isotope.     

New FIR laser lines and frequency measurements for optically pumped CD3OH

Twenty new cw FIR laser lines in CD₃OH, optically pumped by a CO₂ laser, are reported. The frequencies of 39 of the stronger laser lines were measured relative to stabilized CO₂ lasers with a fractional uncertainty, as determined by the reproducibility of the FIR frequency itself, of 2 parts in 10⁷.Contribution of the U.S. Government, not subject to copyright.     

New large offset far-infrared laser lines from CD3OH

The CD₃OH molecule has been investigated for new far-infrared laser lines by optically pumping with a cw waveguide CO₂ laser. The increased tunability (300 MHz) with respect to a conventional CO₂ laser permits to pump many new CD₃OH lines. As a consequence 108 new laser lines have been discovered, ranging from 42.9 to 1155 m in wavelength. On some lines the effect of an electric Stark field has been investigated demonstrating a laser frequency tuning. The total number of known FIR laser lines from CD₃OH is increased to about 340 making this molecule the most prolific together with CH₃OH.     

New FIR Laser Lines from CHD2OH Methanol

We have investigated CHD₂OH methanol as source of far-infrared (FIR) laser radiation using the optical pumping technique. Our new waveguide pulsed CO₂ laser, with peak powers as high as some kW, has allowed us to observe 12 new lines. Each of them is characterized in wavelength, relative polarization, intensity, optimum operating pressure and pump offset from the center of the exciting CO₂ line.     

Measurements and assignments of new large offset CD3OH FIR laser lines

By using an acoustooptic modulator we extend the 300 MHz tunability of a waveguide CO₂ laser to 480 MHz. The CD₃OH was optically pumped by the 10R(32), 10R(34), and 10R(36) CO₂ laser lines, and 17 new FIR laser lines were discovered. The Stark effect on previously known FIR laser lines was investigated, and some tentative FIR laser lines assignments are suggested.