Microwave Lines Research Articles

Observations of Water-Vapor Emission Associated with Infrared Stars

view Abstract Citations (37) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Water-Vapor Emission Associated with Infrared Stars Schwartz, P. R. ; Barrett, A. H. Abstract A survey of 134 infrared stars for microwave H2O emission has resulted in the detection of emission from three new sources: NML Cygni, the Mira variable U Herculis, and the semiregular variable W Hydrae. In all cases the radial velocities of the microwave lines lie between radial velocities of the optical emission and absorption lines of H2O. Publication: The Astrophysical Journal Pub Date: February 1970 DOI: 10.1086/180491 Bibcode: 1970ApJ...159L.123S full text sources ADS | data products SIMBAD (4) Related Materials (2) Erratum: 1970ApJ...160L..61. Erratum: 1970ApJ...160L..61S

Power Saturation of Microwave Line Intensities

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Effect of heat treatment on the electrical resistivity of lithium ferrite

Polycrystalline lithium ferrite samples were subjected to a variety of heat treatments. The most effective process in raising the sample resistivity was the oxidation process. The efficiencies of these heat treatment processes were compared. Effects of heat treatments on the thermoelectric, microwave line width, and dielectric properties of the samples were also reported.

Preparation of [1‐13C], [3‐13C], [1‐D] and [3‐D] Enriched Cyclobutenes

AbstractThree isotopically enriched samples of cyclobutene have been prepared, namely, a mixture containing 20 % [1‐13C]cyclobutene, 20 % [3‐13C]cyclobutene and 60 % parent molecule; a second mixture of 75 % [1‐D]cyclobutene and 25 % parent molecule; and a third mixture of 50 % [3‐D]cyclobutene and 50 % parent molecule. Proton magnetic resonance and infrared spectra showed the samples to be of high purity (> 95 %). The preparations successfully have been used for high‐resolution microwave studies. The observed microwave line intensities also agreed with the percentage compositions given above.

Microwave Line Shape and the Inversion Spectrum of ND3

Microwave Line Shape and the Inversion Spectrum of ND3

Radio observations of interstellar molecules

Investigations of the 18-cm lines of the16O1H radical are still in an exploratory phase. The detection of the strongest line of the18O1H radical has just been reported. Searches for the microwave lines of CH and SiH are in progress.OH absorption has been observed for a few of the stronger radio sources, for a dozen galactic H 11 regions and for the source complex at the galactic centre. The ratio τOH/τHvaries by three orders of magnitude between these sources. In most cases the intensity ratios for the four OH lines are anomalous, which indicates that the populations of the energy levels are perturbed.No thermal emission from OH has been found, even where τ ≈ 1. It thus becomes exceedingly difficult to estimate excitation temperatures and to derive surface densities.Strong non-thermal emission is seen from about a third of the H 11 regions observed. The line profiles are composed of many narrow spikes, quite different for each of the four lines. The intensity ratios of the emission peaks are highly anomalous. The OH emission comes from exceedingly small areas (< 0·1 pc) on theedgeof the ionized regions, with brightness temperatures higher than 106°K.It has been suggested that the populations are inverted. Maser amplification of the background continuum then occurs. Power gains of 104to 105are required. To produce such a gain in a very small region would require high OH densities and a considerable degree of population inversion.In at least eight sources the emission is highly polarized. Complete circular polarization is common, and the sense varies rapidly between adjacent spikes in the profile. The observed polarization is incompatible with Zeeman multiplets.

On the validity of the semi-classical treatment of collisions, in problems of pressure shift and broadening of spectral lines

The semiclassical treatment of pressure broadening of microwave lines, assuming classical straight trajectories and average thermal velocity for the colliding molecules, is obtained as a limit of the quantum impact theory together with its limitations. A model is assumed, according to which collisions with small impact parameter are «strong». The approximations involved in the semiclassical treatment are discussed.

Formation of Hydroxyl Molecules in Interstellar Space

DURING the past year, radio astronomers1,2 have been increasingly interested in microwave signals at frequencies of 1,612, 1,665, 1,667 and 1,720 Mc/s, produced by transitions between four energy levels of the OH molecule in the 2Π3/2 state. Theoretical and laboratory intensity ratios3 for the four microwave lines were found to be 1 : 5 : 9 : 1. It was reported1 recently that anomalous intensity ratios had been measured in the strong OH absorption lines of the radio source Sagittarius A. McGee et al.4 have extended their measurements to other radio sources and find emission and absorption at all four frequencies with instances of extremely anomalous intensity ratios.

Anomalous Intensity Ratios of the Interstellar Lines of OH in Absorption and Emission

WE have previously found1 intensity ratios of the four microwave lines of OH in disagreement with the theoretical and laboratory ratios2 of 1 : 5 : 9 : 1 for the lines at 1,612, 1,665, 1,667 and 1,720 Mc/s. For the strong OH absorption of the radio source Sagittarius A it appeared that the ratios might be attributed to high opacity3. We now report a more detailed series of measurements which shows that high opacity alone cannot account for the observations and that disturbed populations of the levels have to be invoked.

The Doppler contribution to microwave line widths

Although at pressures between 1 and 50 microns the widths of microwave spectral lines are determined primarily by pressure broadening, the Doppler contribution is not insignificant. An expression is derived for the line shape due to the combination of Doppler and pressure broadening, and a method is given for determining the pressure broadening component from the measured width. This method is applied to observations of some inversion lines in the spectrum of ammonia and it is found that collision cross sections deduced from these observations may be in error by up to 8% if the Doppler effect is neglected.

Observations of a Strong Unidentified Microwave Line and of Emission from the OH Molecule

Observations of a Strong Unidentified Microwave Line and of Emission from the OH Molecule

AN ELECTRON SPIN RESONANCE STUDY OF TRAPPED ELECTRONS FORMED AT 77.5 °K BY GAMMA IRRADIATION OF AN ORGANIC GLASS

2-Methyltetrahydrofuran (MTHF) traps electrons and free radicals or radical-ions when irradiated with 60Co gamma rays at 77.5 °K. The e.s.r. difference spectrum technique has been used to determine the microwave saturation properties and line shape parameters of the absorption due to "trapped" electrons. These measurements support the postulate that physically trapped electrons are present and indicate that trapped electrons and free radicals or radical-ions exist in local concentrations which are considerably greater than their average concentration in the sample. It is concluded that they are trapped in clusters. A study of the thermal decay of the trapped electrons supports the cluster model.

Spectrum and Relative Intensities of Interstellar OH Lines

THE initial detection of the OH lines in the interstellar medium involved the two strongest lines at 1,665.402 Mc/s and 1,667.357 Mc/s of the four hyperfine lines making up the 2Π3/2, J = 3/2, Λ-doublet1. Subsequent observations resulted in the detection of the two weaker lines at 1,612.201 Mc/s and 1,720.559 Mc/s2. The strong OH absorption in the direction of the galactic centres, noted by the Australian workers3, and the unexpected disagreement between the theoretical and observed intensity ratios of the lines2, make it important to consider the detection possibilities of other radio lines of OH in the interstellar medium. A discussion of molecular energy-levels and the physical mechanism responsible for the Λ-doublet levels of OH has been prepared for publication elsewhere4; but here we wish to direct attention to 14 microwave lines of various energy-levels and isotopic species of OH, some of which appear to be capable of detection at the present time. The line frequencies, theoretical relative intensities, and transition probabilities are presented in Table 1. The frequencies have been computed by using the theory of Dousmanis, Sanders, and Townes5, and the hyperfine coupling constants given by Radford6. The dipole moment for all isotopic species has been taken to be (1.60±0.12) × 10−18 E.S.U., although this was determined only for 16O1H (ref. 7).

Interdependence of Spectral Line Breadth, Sound Velocity Dispersion, and Viscosity of Small Molecules in the Gas Phase

An examination of the data on bimolecular collisions of small molecules has produced several new insights and predictions. The data on viscosity, sound velocity dispersion, and spectral line breadths in the microwave, infrared, and Raman regions have been assembled for H2, O2, N2, CH3Cl, and HCN. These data have been put on an equivalent basis of calculated or observed spectral line breadth constants. When this is done, the relative importance of elastic and inelastic rotational collisions may be assessed. The data on H2 are here used to predict a collisional narrowing of the ordinary Doppler linewidth; this narrowing effect can be found in the literature, where the significance of the extremely narrow lines has not been fully appreciated. The line breadths observed in the microwave spectrum of oxygen are seen to be peculiar to some phenomenon which reorients electron spins but does not alter rotational states. Spin exchange is here identified as the most probably mechanism for microwave line broadening in O2. The differences between isotropic and anisotropic linewidths in the Raman spectra of H2, O2, and N2 indicate that a thorough theoretical treatment of Raman linewidths is required. Some additional experiments on line breadths in the Raman spectra of H2, O2, and N2 are suggested. The basic approximation in Anderson's impact theory for broadening of spectral absorption and emission lines is seen to be quantitatively invalid for self-broadening of these homonuclear diatomic molecules. This is the approximation of classical (straight) paths. Two new phenomena are predicted for the propagation of rotational energy in small polar molecules. The first of these is a separation of the rotational sound velocity dispersion into two regions for symmetrictop molecules. The region of lower frequency dispersion should account for R/2 of heat capacity, and be associated with changes in rotation about the unique axis of the molecule. Small polar molecules with large dipoles (particularly the alkali halide vapors) should also exhibit a peculiar form of energy propagation in the rotational degrees of freedom only. This ``roton propagation'' may also influence the behavior of shock waves in polar gases and the heat conductivity at very low pressures.

Microwave Line Source for Vacuum Ultraviolet

Microwave Line Source for Vacuum Ultraviolet

Prediction of the field strength fading forms by means of weather situations

In this study the different forms of the electromagnetic field strength recordings at the Thera-Crete microwave line of link are examined, in comparison with the corresponding weather situations prevailing over that area. According to the amplitude of fluctuations, the different forms of recordings have been classified in three basic typesA, B, C and the annual frequency of the appearance of these types has been observed. Finally, the influence of weather situations on radio wave propagation was examined and it has been found that in most cases a close relationship exists between weather situations and the different fading forms of the electromagnetic field so that a prediction of the fading form be possible by means of the weather forecast.

Reaction Kinetics of Polycrystalline Yttrium Iron Garnet

The formation of yttrium iron garnet, Y3Fe2‐(FeO4)3, starting with (1) Fe2O3 and Y2O3 and (2) Fe3O4 and Y2O3, was studied as a function of temperature and time by means of magnetic moment and X‐ray measurements. The reaction began at 600°C. and was completed at 1200°C. The perovskite phase appeared only between 600° and 800°C. Above 1200°C. only the garnet phase was present. The microwave line width and g‐factor at 9303 mc. per second were also measured and related to the preparation variables.

New Method for the Measurement of Microwave Integrated Line Intensities and Line Widths

A method is described for the measurement of microwave line widths and integrated intensities with Stark-modulation spectrometers. The method makes use of a property that the peak intensity αmax,meas, measured at a given Stark field E, depends, under certain conditions, only on the half-width a and the peak intensity αmax. In the present investigation, the method has been used with a Stark cavity spectrometer employing ``antimodulation'' techniques which were described in an earlier paper. Experimental procedure, and the possibilities of the method are illustrated by measurements on two lines arising from the J=1→2 rotational transition of the 16O12C32S molecule in the ground state, and in the excited bending-vibrational state (l-doublet). The measured integrated intensity of the ground-state line of (103±3.5)10—5 cm—1 sec—1 at 1 mm Hg agrees well with the theoretical value of 101.5·10—5 cm—1 sec—1. The half-width constant of the ground-state line and of the l-doublet line was found to be 6.27±0.18 and 6.17±0.23 Mc/mm Hg, respectively. From the measurements on the various mixtures of OCS and N2, a value of 4.36±0.12 Mc/mm Hg has been obtained for the collision broadening factor for OCS molecules with N2 molecules. The present method is applicable to sharp (also weak) lines of which the Stark splitting pattern is quantitatively known.

Galactic structure and the 21-centimetre microwave line

Galactic structure and the 21-centimetre microwave line

Generalization of the One-Dimensional Ising Model Applicable to Helix Transitions in Nucleic Acids and Proteins

The exact treatment of the Ising model for an infinite, one-dimensional system has been generalized to make it applicable to the helix transition in synthetic polynucleotides, DNA, synthetic polypeptides, and proteins. The particular advantages of the present treatment are flexibility and generality: the free energies of sequences of similar units of any size can be assigned arbitrary values in the final equations; also ``mismatching'' between the two strands in a double helix is allowed for. Anderson's general theory of collision line broadening has been applied to H2O–N2 encounters. The only attractive force was assumed to be that between the H2O dipole, μ=1.87×10—18 esu, and the N2 quadrupole, qN2, an adjustable parameter. A second adjustable parameter, bm, the distance of closest approach, includes the effects of all other forces. The IBM 704 was used in the calculation. Effects of varying the parameters were noted for a number of lines, and in the final calculation, which yielded the widths of all significant type B transitions up to J″=13, parameters qN2=2.62×10—26 esu and bm=3.2 A which give an exact fit of the observed width of the microwave line 6—5—5—1, were adopted. The temperature dependence of the line width over the range 220–2400°K, and the effects of vibration-rotation interactions were also calculated. At 300°K widths vary from 0.11115 cm—1 atmos for 11—1—1 to 0.03200 cm—1 atoms—1 for 14—13—13—13, there being a general decrease in width with increasing J, and at a given J, decreasing width with increasing τ.