Far infrared fine structure lines in the interstellar medium

Fine structure lines in the far-infrared have many simple properties that make them useful tools for diagnosing astrophysical plasmas. The line ratios are sensitive and accurate probes of density, elemental abundances, and ionization structure. In addition, studies of line shapes and Doppler shifts should prove valuable in studies of the gross dynamics of H II regions and galaxies. We present a review of the theory involved in the interpretation of these lines, and a summary of the observations made so far.Work supported in part by NASA grant NGR 05-003-511.     

Far infrared emission spectra from stratospheric hydrogen peroxide

Synthetic emission spectra from two stratospheric altitude observations have been analyzed for the presence of H₂O₂ in the far infrared region. The calculations are made with a high spectral resolution (10^–3 cm^–1 or 10^–4 cm^–1) greater than those in experimental measurements which are in the region of 3.10^–3 cm^–1. Spectra cover a spectral interval between 40 and 120 cm^–1 showing the best features of H₂O₂ susceptible to observation in a stratospheric spectrum. The optimum conditions for identification have been considered. Using the variations in H₂O₂ abundance in the measurement data and photochemical models, the H₂O₂ features detection limits have been studied.     

New far infrared measurements of the rotational spectrum of cyanoacetylene HC3N

Several rotational lines of cyanoacetylene in the ground state and the first excited state v7=1 have been measured between 580 and 1100 GHz with a new FIR laser sidebands spectrometer. A global analysis which takes into account the previous measurements on this molecule is performed.     

Far infrared spectrum of acrylonitrile

Two bands in the far infrared spectrum of acrylonitrile have been studied under moderately high resolution. Accurate band centers are obtained and the rotational constants are analyzed in terms of Coriolis coupling between the in-plane and out-of-plane bending modes.     

The Current Development of Far Infrared Technology

The research development and the latest results of far-infrared laser in the last few years were introduced from the following aspects: far-infrared laser, study of basic science, study of astrophysics, communication and military applications, engineering applications, study of medical biology and other applications.     

A Note on CH3OD Spectra, Ground-State Energies and FIR Laser Assignments

Literature data on the CO-stretching and the ground-state torsion-rotation spectra of the CH₃OD isotopic species of methanol have been exploited to extrapolate the ground-state energies to higher J through use of ground-state combination differences derived from the CO-stretching wavenumbers. In particular, the J-dependence has been extended and better defined for the difficult |K| = 0 to 2 E energy level sequences, which are strongly affected by molecular asymmetry. The pattern of the J-dependence is found to be qualitatively well reproduced by a simple 11 × 11 Hamiltonian model incorporating K = ±1 and ±2 off-diagonal asymmetry matrix elements. The results suggest partial reassignment of certain CO-stretching subbands, and the K = 8 and 9 A subbands have been newly identified through clues from reported far-infrared laser (FIRL) emission. Transition combination loops support a number of FIRL line assignments previously proposed, but show that the FIRL system pumped by the 9R(4) CO₂ line must be reassigned.     

Torsional refilling transitions in tea-pumped CH3OH fir lasers with associated high-resolution fir spectra

It is proposed that a number of the high-frequency far-infrared (FIR) laser lines observed when CH₃OH is optically pumped by high-power CO₂ TEA lasers can be identified as refilling torsional transitions within the vibrational ground state. Assignments are presented for 8 such TEA-pump/FIR-laser refilling systems. To provide support for the assigned laser frequencies, high-resolution Fourier transform FIR spectra of CH₃OH have been obtained and partially analyzed in the torsional transition region.     

High-resolution far-infrared spectroscopy of C-13 methanol

The high-resolution far-infrared (FIR) Fourier transform spectrum of¹³CH₃OH has been studied from 25–350 cm^–1, andb-type^rR-branches in the torsional ground state have been assigned. The branches have been fitted to phenomeno-logical expansion parameters, which reproduce the branch frequencies generally to well within ±0.001 cm^–1. An interesting and relatively novel K=4 perturbation, localized to levels around J=18, has been observed between (nK)=(019) and (125) states.     

Far infrared laser thermal spectroscopy of superconductors

An optically pumped far infrared laser provides fixed photon energies near the superconducting gap, making it possible to carry out experiments where the temperature is swept through T_c. Such thermal measurements in thin films of V₃Si show both known and unexplained features, with some of the latter perhaps due to a second gap. The thermal technique shows potential for the study of superconductors.Work supported by the U.S. Department of Energy under Contract No. DE-AS05-79ER10436.     

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.     

Rotational spectrum of trifluoroacetone

The rotational spectra of 5 isotopologues of 1,1,1-trifluoroacetone have been assigned using pulsed-jet Fourier-transform microwave spectroscopy. All rotational transitions appear as doublets, due to the internal rotation of the methyl group. Analysis of the tunneling splittings using both the principal axis method (PAM) and the combined axis method (CAM) methods allows to determine accurately the height of the threefold barrier to internal rotation of the methyl group, and its orientation, leading to V₃ = 3.28 and 3.10 kJ mol⁻¹, respectively. The r_s geometry of the molecular skeleton, a partial r₀ structure of the molecule and supporting ab initio calculations are also reported.     

Far infrared laser magnetic resonance spectrum of CH

Laser magnetic resonance spectra between 0 and 17 kG have been recorded and analyzed for $\text{(J′ ← J″) = (}\text{7}\text{2}\text{←}\text{5}\text{2}\text{)}$, $\text{(}\text{5}\text{2}\text{←}\text{3}\text{2}\text{)}$, and $\text{(}\text{3}\text{2}\text{←}\text{1}\text{2}\text{)}$ transitions in the CH molecule, using the optically pumped far infrared lasers: 118.8 μm (CH₃OH), 180.7 μm (CD₃OH), 554.4 μm (CH₂CF₂), 561.3 μm (DCOOD), and 567.9 μm (CH₂CHCl). Other transitions in CH were detected with the ¹³CH₃OH laser at 115.8, 149.3, and 203.6 μm. The CH radical was generated in a low-pressure methane and atomic fluorine flame within the laser cavity. Analysis of the M′_J ← M″_J structure yields wavenumbers for the rotational transitions mentioned above of 84.3494, 55.3397, and 17.8376 cm^?1, respectively. Combining results from the M_J analysis with the $\text{J =}\text{1}\text{2}\text{Λ-}\text{doubling}$ interval derived from radioastronomy measurements yields Λ-doubling values for the $\text{J =}\text{3}\text{2}\text{,}\text{5}\text{2}$, and $\text{7}\text{2}$ states of 0.0237, 0.1620, and 0.3759 cm^?1, respectively. Both the rotational intervals and the Λ-doublings are in good agreement with earlier less precise optical results. Analysis of the hyperfine structure yields values for the Frosch and Foley hyperfine parameters of a = +52, b = ?74, c = +52, and d = +43.6 MHz, in good agreement with recent ab initio estimates and radioastronomy measurements.     

Kinetics of irreversible transformations in a glassy crystal studied by infrared spectroscopy

The kinetics of the transformation between phases I, II and III of solid cyclohexanol was studied by Fourier transform infrared spectroscopy. Special attention was paid to the dependence of the time evolution on the thermal history of the sample. We observed drastic change of the kinetics after 48 hours of aging in the glassy state. The time evolution of the spectra was described by a power low rather than an exponential one.     

Torsion-rotation far-infrared spectrum of O-18 methanol

High-resolution Fourier transform spectra have been recorded from 15–470 cm^–1 for the far-infrared trosion-rotation band of O-18 methanol in the vibrational ground state. So far, 57 subbands have been assigned in the 15–220 cm^–1 region for a wide range of rotational and torsional states, and their J-independent origins have been determined to an estimated accuracy of ±0.01 cm^–1. The observed origins were found to deviate in many cases by several tenths of a cm^–1 from the values calculated with the previous molecular parameters. Together with 4 known microwave origins, the new data have been fitted to a model torsion-rotation Hamiltonian in order to refine the set ofb-type molecular constants for the ground state. With the new parameter set, the experimental subband origins are reproduced with an rms error of ±0.02 cm^–1, representing a substantial improvement over the earlier situation. The spectroscopic results have also been of great assistance with our assignments of optically-pumped FIR laser emission in CH₃ ¹⁸OH, in providing FIR data for checking the identification of the IR-pump/FIR-laser transition systems through combination loop relations.     

Far Infrared Spectroscopic Studies of Acetonitrile Vapour

Abstract

The infrared spectrum of acetonitrile vapour has been obtained in the range below 100 cm^?1. There is an absorption band located at 78 cm^?1 which is assigned to overlapping intermolecular vibrations of dimer molecules in equilibrium with the monomer species. The equilibrium constant calculated from the pressure dependence of the band intensity amounts to 42 ± 26 1·mol^?1.     

Microcomputer control and data analysis for a far infrared Fourier spectrometer

A commercial general-purpose microcomputer is used to provide real-time experimental control, data acquisition and data analysis for a far infrared Fourier spectrometer. The interfacing and programming procedures are described. The microcomputer gives excellent performance at a low cost.     

Ritz assignment and Watson fits of the high-resolution ring-puckering spectrum of oxetane

Oxetane is a four-membered ring molecule exhibiting a large-amplitude ring-puckering motion. In order to analyze this vibration we recorded a rotationally resolved far-infrared spectrum between 50 and 145 cm⁻¹. The analysis of the ring-puckering fundamental band with the assignment of 1108 lines, has been presented in a previous paper. In the present work we present a list of further 6531 assigned transitions between the five lowest excited ring-puckering states. The 4983 term values involved in the transitions assigned in this and in the preceding work have been evaluated by the “Ritz” program, and are now available. An A-reduced Watson Hamiltonian in any of the three representations I^r, II^r, and III^r was used to perform a fit of the assigned transitions. Precise rotational constants and quartic as well as a full set of sextic centrifugal distortion constants were obtained for the investigated ring-puckering states. For the first time, high-resolution values for the vibrational G_v parameters have been obtained, and we have added terms in x⁶ and x⁸ to the double minimum-potential well describing the ring-puckering motion, in order to reproduce their values within the experimental accuracy. The same potential still reproduces the lower resolution values of the Q-branch origins involving higher ring-puckering states up to v_rp=14 found in the previous literature.