Experimental investigation of13CD3OH infrared transitions by means of optoacoustic spectroscopy

A systematic investigation of¹³CD₃OH infrared transitions around CO₂ laser line emissions is performed by means of optoacoustic detection. Using a waveguide CO₂ laser of 290 MHz tunability and, in some cases, an acoustooptic modulator to provide an extension of 180 MHz, 108 transitions are observed. Measurements of pump off-set and relative intensity have been performed. The data may be compared with those previously reported of high resolution Fourier Transform spectroscopy.     

Laser stark spectroscopy of CD3OH and13CH3OH at 311μm

Laser Stark spectra have been observed for CD₃OH and¹³CH₃OH using the 311 μm line of the HCN laser. The spectra were taken for both parallel and perpendicular polarizations up to 60,000 Volts/cm. For CD₃OH, the two characteristic structures in the spectra have been identified as the J_K=14₄←13₃, A^± doublet in the v_t=0 torsional state. For¹³CH₃OH, the low field structure observed is assigned as J_K=15₃←14₂, A^? in the v_t=0 torsional state.

     

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.     

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.     

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.     

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,υ _t=0; J _k =11₄ ← 10₃ E _l ,υ _t=0; and J _k =17₃ ← 16₂ E₂,υ _t=0 have been identified while the assignments for¹³C-substituted methanol are J _k =14₈ ← 15₇ A,υ _t=0; J _k =15₃ ← 14₂ A⁺,υ _t=0; J _k =10₇ ← 9₆ A,υ _t=0; and J _k =27₉ ← 27₈ E₁,υ _t=0. Zero-field frequencies for the assigned transitions are given with improved accuracy over those calculated from available molecular constants, especially for¹³CH₃OH.     

Microwave spectra of CD3OH methanol

The microwave spectrum of CD₃OH has been studied over the 8 to 58 GHz region, and numerousb-type transitions have been assigned. Many of these belong toP subbranches which descend to the microwave region from subband origins lying much higher in the far-infrared, pass through zero frequency, and return upward again. Others are members ofb-typeQ branches which extend across the region. As well, variousa-typeK-doublet lines arising as transitions directly across the split levels of asymmetry doublets have been identified.     

Identification of the high efficiency 127μm FIR laser line of13CD3OH

An assignment is proposed for the strong 127.0 μm far-infrared (FIR) line of¹³CD₃OH known to be pumped with very high efficiency by the 10P(8) CO₂ laser line. On the basis of spectroscopic clues derived from calculated molecular parameters and energies for¹³CD₃OH, the 127 μm line is identified as the (nτK,J)=(116,17)→(125, 16) transition, and its companion 462.8 μm line as the (116,17)→(116,16) transition. Proposed partial assignments and predictions are also discussed for a number of other FIR laser lines in¹³CD₃OH, CD₃OH, CD₃OD, CH₃OD, CH₃OH and¹³CH₃OH.     

New FIR Laser Lines from CD3OH

Fourteen new optically pumped far-infrared (FIR) laser lines in the range 46.8 μm to 172.6 μm were discovered in optically pumped CD₃OH. The pump sources include both the CO₂ laser and the N₂O laser. Two theoretically predicted laser lines were observed in this study.     

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.     

FIR laser assignments and frequency predictions for optically pumped13CD3OH by high-resolution Fourier transform spectroscopy

Continued study of the high-resolution Fourier transform spectroscopy (FTS) of the fundamental CO-stretching band of¹³CD₃OH has given additional insight into the far-infrared (FIR) laser emission observed when this molecule is optically pumped by a CO₂ laser. Eleven IR-pump/FIR-laser transition systems are considered. Seven represent completely new assignments, while four have been presented previously but are discussed further with reference to recently reported experimental data. Ten of the assignment schemes have been rigorously checked by forming closed combination loops, and accurate FIR laser wavenumbers have been obtained. The superiority in precision of the FIR laser wavenumbers determined from FTS combination loops over those from traditional wavelength measurements is demonstrated.     

Far infrared spectrum of CD3OH methanol from 40–220 CM−1

The Fourier transform far-infrared (FTFIR) spectrum of CD₃OH has been obtained from 40–220 cm^?1 at a resolution of 0.002 cm^?1, and partially analyzed. Numerousb-type branches have been assigned in the spectrum, ranging over torsional states fromn=0 to 3. The branches have been fitted toJ(J+1) power-series energy expansions in order to obtainJ-independent branch origins. These in turn have been fitted to the torsion-rotation Hamiltonian, and improved molecular constants have been obtained for the ground vibrational state.     

Measurement of Laser Frequencies from CD3OH and CD3OD up to 8.6 THz

Twenty two laser frequencies, whose values range from 1.6 to 8.6 THz, have been measured for the first time using heterodyne techniques. These laser emissions were generated by an optically pumped molecular laser that used either CD₃OH or CD₃OD as its lasing medium. At least three of the observed laser emissions generated by CD₃OH were discovered during this investigation and the first laser frequencies measured for CD₃OH above 8 THz are reported. The laser frequencies were measured with fractional uncertainties up to ± 2 × 10^?7, of sufficient accuracy to confirm two proposed far-infrared laser assignments. The offset frequency of the CO₂ pump laser with respect to its center frequency was also measured for nearly all laser emissions generated by CD₃OH.     

Electric field effects on the efficiency of optically pumped submillimeter lasers

The FIR power dependence on an applied electric field is carefully investigated for optically pumped lasers. The enhancement effect observed for many laser lines, both "orthogonal" and "parallel," is analyzed as a function of different parameters such as gas pressure, laser threshold, cavity tuning, and transitions selection rules. Measurements of the IR absorption of the gases are also carried out by a Stark optoacoustic technique. Absorption increases are observed at low electric field values. The experimental results disagree with the previously proposed linear Hanle effect explanation. They are explained with the increase in the pump saturation intensity, also detected with the transferred Lamb-dip technique. The combined effects of the absorption increase and of the small-signal gain curve decrease are shown to qualitatively explain the observed FIR enhancement features.     

New optically pumped FIR laser lines in CD3OH

In this work we report laser action in 69 new FIR laser lines in CD₃OH optically pumped by a regular cw CO₂ laser. We have performed measurements of laser wavelength, optimum pressure of the gas, relative polarization and intensity on all lines, including some previously known.     

Vibrational and Rotational Spectroscopy of 13CD3OD

We have used Fourier Transform spectral data on the C-O stretching mode of ¹³CD₃OD in order to perform a vibro-rotational analysis for this molecule. We have estimated a few molecular parameters of the ground and C-O stretching vibrational modes. Based on these parameters, and by using the Kwan-Dennison model, we propose assignments for a number of far-infrared laser transitions of ¹³CD₃OD.     

Observation and assignment of torsional transitions in FIR emission from optically pumped CH3OH

Using output coupling by reststrahlen reflection from NaCl we have observed 14 new FIR lines in the wavelength range between 30 μm and 60 μm. Two of them have been identified as torsional n=1→0 transitions in the CO stretch vibration. Together with lines previously reported in the literature they are the basis for an identification of 41 FIR lines associated with torsionally excited states.     

Electric field effects in AlGaAs-GaAs symmetric and asymmetriccoupled quantum wells

A theoretical study of energy level shift and field-induced tunneling in symmetric and asymmetric coupled quantum wells is presented. Energy level shift is calculated from the time-dependent Schrodinger equation using the inverse power method. The time evolution of an electron wavepackage is shown by the application of the time-development operator of the time-independent Schrodinger equation. Energy level shift in coupled quantum wells is found to be enhanced in comparison to single quantum wells. The energy level shift in coupled quantum wells is found to be nearly linear with the applied field. Oscillation frequencies for electrons in symmetric and asymmetric coupled quantum wells are evaluated versus the applied field and compared to semiclassical prediction. Tunneling lifetimes in symmetric and asymmetric coupled quantum wells are evaluated versus the applied field