Collisional broadening and shifting of OCS rotational spectrum lines

Broadening and shifting of carbonyl sulfide (OCS) rotational spectrum lines by pressure of N₂, O₂ and OCS were accurately studied in the frequency range 24–850 GHz at room temperature using a spectrometer with radio-acoustic detection of absorption. Rotational dependences of collisional widths of OCS spectrum lines were determined by a simple empirical polynomial fit of experimental data. Experimental uncertainties were analyzed. Results of supplementary test measurements of self-broadening of rotational OCS lines in the ν₂ excited vibrational state and carbon monoxide (CO) lines in the ground vibrational state are presented. Comparison of the obtained results with previously known measurements and theoretical calculations is given. The performed work allows for the first time development of accurate gaseous etalon of absorption for atmospheric applications and laboratory use, covering continuously the whole millimeter- and submillimeter-wave range.     

A combined ab initio, Fourier transform microwave and Fourier transform infrared spectroscopic investigation of β-propiolactone: The ν8 and ν12 bands

The pure rotational spectrum of β-propiolactone (c-C₂H₄COO) has been recorded between 7 and 21 GHz using a pulsed jet Fourier transform microwave spectrometer. The resulting ground state spectroscopic constants guided the analysis of the rotationally-resolved infrared spectra of two bands that were collected using the far infrared beamline at the Canadian Light Source synchrotron. The observed modes correspond to motions best described as ring deformation (ν₁₂) at 747.2 cm⁻¹ and CO ring stretching (ν₈) at 1095.4 cm⁻¹. A global fit of 4430 a- and b-type transitions from the microwave spectrum and the two infrared bands provided an accurate set of ground state and excited state spectroscopic parameters. To complement the experimental results, the harmonic and anharmonic vibrational frequencies of all 21 infrared active modes of β-propiolactone have been calculated using the DFT B3LYP method (6-311+G(d,p), 6-311++G(2d,3p) basis sets).     

Millimeter- and Submillimeter-Wave Spectra of CD2F2

The millimeter- and submillimeter-wave spectrum of ¹³CD₂F₂ present in natural abundance in methylene fluoride-d₂ (CD₂F₂) has been measured in the region 230-380 GHz. The spectrum was recorded using a frequency-modulated millimeter- and submillimeter-wave spectrometer. More than 200 rotational transitions in the ground state of ¹³CD₂F₂ with J≤45 and K_a≤8 have been assigned. A combined weighted least squares fit of the newly assigned transitions with previously reported microwave data has been carried out in the Watson's A- and S-reduced Hamiltonian. The data have been fitted with a standard deviation approaching the experimental accuracy, to provide improved values for the rotational and quartic centrifugal distortion constants, including sextic distortion constants for the ground state of ¹³CD₂F₂.     

Analysis of ν2 of H2Se

The infrared absorption spectrum of ν₂ of H₂Se in the region from 885 to 1347 cm^?1 was obtained with a resolution limit of 0.025 cm^?1 on the University of Denver 50-cm FTIR spectrometer system. We have assigned 1604 lines for the six isotopomers of H₂Se, including 25 lines for the H₂⁷⁴Se isotopomer, and have analyzed them using Watson's A-reduced Hamiltonian in the I^r rotational representation. Ground state constants for each of the five most abundant isotopomers were obtained from fits of microwave transitions combined with weighted averaged ground state combination differences formed from the infrared bands (010), (020), (100), and (001). Upper state constants for each of the five most abundant isotopomers were obtained from least-squares fits of the spectral lines of ν₂, keeping the ground state constants fixed to the values determined from our ground state fits. An alternate set of ground state constants together with isotopic mass adjustment constants for all six isotopomers was determined by simultaneously fitting all available microwave transitions and infrared ground state combination differences. Keeping this set of ground state constants fixed, a single set of upper state constants and isotopic mass adjustment constants for the ν₂ band was determined by a simultaneous fit of infrared spectral lines from all six isotopomers.     

Pure Rotational Spectra of SO: Rare Isotopomers in the 80-GHz to 1.1-THz Region

Pure rotational spectra of rare isotopomers of sulfur monoxide, SO, have been recorded with the Cologne Terahertz Spectrometer, Germany, and the millimeter- and submillimeter-wave spectrometer at Nobeyama, Japan. In total, 176 new transitions have been measured in theX³Σ⁻electronic ground state, including the first laboratory detection of the rare isotopomer³⁶SO. New lines are also reported for³³SO and S¹⁷O in their vibrational ground states, and for³³SO and S¹⁸O in the first excited vibrational state. A simultaneous fit of 451 transitions has led to an improved set of isotopically invariant parameters for rotation and fine structure. Hyperfine structure constants for³³SO and S¹⁷O have been obtained also from the global fit, including first values for the magnetic nuclear spin–rotation interaction. These are compared to other molecules. The isotopically invariant parameters allow precise frequency predictions for the submillimeter-wave region far beyond 1 THz for all SO isotopomers, of importance to astrophysical applica- tions.     

High resolution fourier transform spectroscopy using infrared synchrotron radiation: I. Instrumentation

A compact high resolution (.002 cm^–1) vacuum Fourier transform spectrometer for use with far infrared synchrotron radiation was constructed at the National Synchrotron Light Source at Brookhaven National Laboratory. The spectrometer may be operated using a gas cell of path length of 2 m and a He cooled bolometer with NEP of 10^–13. The pure rotational spectrum of Ammonia was used to test the spectrometer.     

The Microwave Spectrum of Methyl Formate (HCOOCH3) in the Frequency Range from 7 to 200 GHz

The rotational spectrum of methyl formate (HCOOCH₃) has been observed in the frequency range from 7 to 200 GHz. We newly assigned 1612 lines in the ground torsional state and simultaneously analyzed both A- and E-species data including previously reported lines on the basis of the internal axis method. A total of 3077 lines were fitted to a 1σ standard deviation of 139 kHz, and molecular parameters were determined.     

Far infrared spectrum of methylamine

The far-infrared (FIR) spectrum of CH₃NH₂ has been studied in the 25–125 cm^–1 region at a resolution of 0.005 cm^–1 with a BOMEM Fourier transform spectrometer. All of the^rR branches with K rotational quantum number from 5 to 13 have been identified for A-a and E-a torsion-inversion symmetries in the ground torsional state, as well as some branches of A-s and E-s symmetries and some in excited torsional states. The observed branches have been fitted to series expansions in order to determine the branch origins.     

Generation of Submillimeter-Wave Radiation with GaAs Tunnett Diodes and InP Gunn Devices in a Second or Higher Harmonic Mode

Efficient second-harmonic power extraction was demonstrated recently with GaAs tunnel injection transit-time (TUNNETT) diodes up to 235 GHz and with InP Gunn devices up to 325 GHz. This paper discusses the latest theoretical and experimental results from second-harmonic power extraction at submillimeter-wave frequencies and explores the potential of using power extraction at higher harmonic frequencies to generate continuous-wave radiation with significant power levels at frequencies above 325 GHz. Initial experimental results include output power levels of more than 50 W at 356 GHz from a GaAs TUNNETT diode in a third-harmonic mode and at least 0.2–5 W in the frequency range 400–560 GHz from InP Gunn devices in a third or higher harmonic mode. The spectral output of these submillimeter-wave sources was analyzed with a simple Fourier-transform terahertz spectrometer and, up to 426 GHz, with a spectrum analyzer and appropriate harmonic mixers. Initial experimental results from a GaAs/AlAs superlattice electronic device at D-band (110–170 GHz) and J-band (170–325 GHz) frequencies are also included.     

Rotational Spectrum of Vinylarsine

The rotational spectrum of vinylarsine in the ground state has been studied in the range 7–320 GHz. The spectra of asynconformer and agaucheconformer have been unambiguously assigned on the basis of the existence of ab-type or ac-type spectrum. Rotational constants, quartic, and some sextic centrifugal distortion constants were derived. For thesynform, measurements of lowJ^aR_0,1transitions in a pulsed-nozzle Fourier transform microwave spectrometer (FTMWS) enabled the determination of the diagonal elements of the quadrupole tensor, as well as two spin–rotation constants.Ab initiocalculations performed at the MP2 level using the 6-311++G(3df, 3pd) basis set reproduced experimental rotational constants within 0.2%.     

Double resonance and collision-induced transitions in the radiofrequency spectra of H2CO and HDCO observed inside the cavity of a CO2 laser

Many radiofrequency resonances corresponding to transitions between the two components of a K-type doublet in H₂CO and HDCO have been observed using infrared-radiofrequency double resonance inside a CO₂ laser cavity. For strong resonances, additional transitions induced by collisions have also been observed and these provide information on collisional processes. The collision-induced transitions also provide a method for assigning the K doublet frequencies in the ground and v₄ = 1 states of H₂CO, and in the ground, v₅ = 1, and v₆ = 1 states of HDCO; the rovibrational transitions pumped by the CO₂ laser can therefore be determined. The upper state rotational transitions and the infrared frequencies for the transitions in exact coincidence with the CO₂ laser lines provide accurate additional data in the analysis of the conventional infrared spectrum of the ν₅ and ν₆ bands of HDCO. In addition, the 195-μm far-infrared laser line in HDCO, observed by Dangoisse et al. [J. Quantum Electron. QE-13, 730–731 (1977)] has been assigned as the 24_6,19→23_6,18 transition in the v₆ = 1 state.     

THz spectrum of monodeuterated methane

We report new measurements of the rotational spectrum of monodeuterated methane (CH₃D) in the range of 690-1200 GHz which allow for an accurate prediction of all lines in the range of the high-resolution spectrometer of the Herschel Space Observatory. Comparison is also made with the previous analysis based on infrared combination differences. Three lines of ¹³CH₃D were measured in natural abundance.     

Far infrared pure rotational spectrum of methylacetylene

The pure rotational spectrum of methylacetylene has been recorded in the far infrared region between 10 and 60 cm^?1 with a Fourier transform spectrometer whose theoretical resolution was 0.025 cm^?1. From the measured wavenumbers it has been possible to determine the rotational constants in the ground state and in the v₅ = 1, v₈ = 1, v₁₀ = 1, 2, 3, 4 levels.     

Pressure shift and broadening of 110-101 water vapor lines by atmosphere gases

This paper is devoted to the measurement of pressure shift and broadening parameters of water-vapor lines of the pure rotational transition 1₁₀-1₀₁ in the ground vibrational state of H₂¹⁶O at 556.936 GHz, H₂¹⁷O at 552.02 GHz, H₂¹⁸O at 547.676 GHz, and the vibrationally excited state v₂=1 line of H₂¹⁶O at 658.003 GHz. The broadening coefficients of the line at 556.936 GHz (for N₂ and O₂ as perturbing gases) coincide within the errors with the values obtained recently by Seta et al. [Pressure broadening coefficients of the water vapor lines at 556.936 and 752.033 GHz. JQSRT 2008;109:144-50] by means of a very different technique (THz-TDS). Pressure shift and broadening for other lines were measured for the first time. Comparison of our results with previous measurements and theoretical calculations is presented.     

THz spectroscopy of H2D

The 2₁₂ − 1₁₁ line of H₂D⁺ at 2.363 THz that was detected toward Sgr B2 and identified based on a calculated line frequency has been measured in the laboratory precisely by using a tunable far-infrared spectrometer. All the available THz lines and known millimeter- and submillimeter-wave lines together with the combination differences derived from the infrared transitions are fitted to the Watson effective Hamiltonian. A set of improved molecular constants are obtained.     

Microwave spectrum and structure of furfural

The microwave spectrum of furfural was investigated in the frequency range 7 GHz-21 GHz and 49 GHz-330 GHz. The ground and first torsional state of trans-furfural and ground state of cis-furfural were assigned and analyzed. A total of 1720 rotational lines with J up to 100 and K_a up to 53 were assigned to the ground state of trans-furfural, 1406 rotational lines with J up to 100 and K_a up to 48 were assigned to the first torsional state of trans-furfural and 2103 rotational lines with J up to 90 and K_a up to 48 to the ground state of cis-furfural. Accurate sets of centrifugal distortion constants for both conformations have been determined for the first time. The spectra of all ¹³C and ¹⁸O singly substituted isotopic species were observed in natural abundance in the 7 GHz-21 GHz range. Molecular structure co-ordinates, bond lengths and angles of the Kraitchman substitution type (r_s) and pseudo-Kraitchman type (r_pKr) are derived from the isotopic studies.     

Fourier-transform microwave and submillimeter-wave spectroscopy of chloroiodomethane, CH2ICl

Guided by a previous microwave study (9–35 GHz), the rotational spectrum of both chlorine isotopologues of chloroiodomethane in its vibrational and electronic ground state has been re-investigated in the microwave region and extended to the millimeter/submillimeter-wave region. Weak a-type transitions have been recorded by Fourier transform microwave spectroscopy below 20 GHz whilst strong b-type rotational transitions have been recorded between 15 and 646 GHz, corresponding to energy levels with J″ ≤ 108 and . Molecular constants including those describing the hyperfine structures owing to the two halogen atoms were accurately determined for both species from the least-squares analysis of a total of 1475 distinct transition frequencies (of which 906 belong to the CH₂I³⁵Cl isotopologue). The two sets of rotational constants allowed us to derive an r₀ structure of CH₂ICl.     

Hyperfine Interaction Constants of the HCCS and DCCS Radicals Studied by Fourier Transform Millimeter-Wave Spectroscopy

The rotational spectral lines of HCCS and DCCS have been observed with a Fourier transform millimeter-wave spectrometer in combination with a pulsed discharge nozzle. The HCCS radical is produced by discharging a mixture of C₂H₂ and CS₂ diluted in Ar. The DCCS radical is produced by using C₂D₂ instead of C₂H₂. The spectral lines of HCCS and DCCS in both the ²Π_3/2 and ²Π_1/2 states are measured in the frequency range from 16 to 48 GHz, and the molecular constants are determined accurately from a joint least-squares analysis with the reported millimeter- and submillimeter-wave data. The hyperfine interaction constants of the hydrogen and deuterium nuclei are determined for the first time, and are discussed in relation to the Renner-Teller effect on this molecule.     

Terahertz Spectroscopy of the Amidogen Radical, NH2

The rotational spectrum of the NH2 radical in its &Xtilde;2B1 ground vibronic state was investigated between 614 and 1003 GHz. One hundred fifty-nine newly observed lines (188 hyperfine components) of six rotational transitions with 0 相似文献   

Laser magnetic resonance of the O2 molecule at 699 μm

A new highly sensitive far infrared optically pumped laser magnetic resonance (LMR) spectrometer has facilitated the observation of 21 transitions in O₂ at 699 μm (428.6285 GHz). All of these transitions involve N = 3 ← 1 of the oxygen molecule in its electronic ground state, X³Σ_g⁻. Of these 21 lines, 10 are due to the ¹⁶O₂, v = 0; 5 are due to the ¹⁶O₂, v = 1; 5 are due to the ¹⁶O¹⁸O, v = 0; and 1 set of 6 hyperfine components is due to the ¹⁶O¹⁷O, v = 0. From the intensity of the observed lines the sensitivity limit of this LMR spectrometer is found to be about 10⁻⁹ cm⁻¹ at this frequency with a 1-sec time constant.