Engineering topics
Publications and source records attributed to Cohen, E. A..
The N 2 and O 2 pressure broadenings of the CIO transitions near 204 and 649 GHz have been measured between 200 and 300 K. Oxygen broadening has been measured for the transitions near 278 GHz.
The rotational spectra of the 2Sigma(2+) ground states of calcium monohydride and monodeuteride have been recorded in absorption between 250 and 700 GHz. The gas phase free radicals have been produced in a ceramic furnace by the reaction of elemental calcium with molecular hydrogen or deuterium in the presence of an electrical discharge. The molecular constants including the rotational constant, centrifugal distortion constants, spin-rotation constants, and magnetic hyperfine interaction constants have been extracted from the spectra.
The N2 and O2 pressure broadenings of the two O3 transitions, which are used for satellite monitoring of upper atmospheric O3, have been measured between 200 and 300 K. The derived air-broadening coefficients are accurate within 3 percent over the entire temperature range.
A computer-accessible catalog of submillimeter, millimeter, and microwave spectral lines in the frequency range between 0 and 10,000 GHz (i.e., wavelengths longer than 30 micrometers) is described. The catalog can be used as a planning or as an aid in the identification and analysis of observed spectral lines. The information listed for each spectral line includes the frequency and its estimated error, the intensity, the lower state energy, and the quantum number assignment. This edition of the catalog has information on 206 atomic and molecular species and includes a total of 630,924 lines. The catalog was constructed by using theoretical least square fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariances. Future versions of this catalog will add more atoms and molecules and update the present listings as new data appear. The catalog is available as a magnetic data tape recorded in card images, with one card image per spectral line, from the National Space Science Data Center, located at Goddard Space Flight Center.
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These transitions are forbidden in the sense that they follow the selection rule delta K = + or - 2, which violates the usual rule that delta K = + or - 1 for a perpendicular band of a symmetric top, where K is the projection of the total angular momentum onto the molecular symmetry axis. The assignments are based for the most part on laser-Stark measurements made with a CO laser and an intracavity Stark cell. The procedure followed in making the assignments is described. Attention is called to the significance of these new lines in the analysis of the nu-4 vibrational state and in an improved determination of the ground-state rotational and centrifugal distortion constants.
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An additional 86 lines of the NH2D rotation-inversion spectrum were measured between 7.5 and 850 GHz. These data and the existing NH2D and ND2H data are fitted to a Hamiltonian in which the vibration-rotation interaction is included in the form of an off-diagonal inertial tensor term. For comparison with the symmetric ammonias an oblate basis and a Watson-type reduced 'S' set of distortion constants are used. A theory for the interaction term is given which is in excellent agreement with experiment. Structural parameters are derived. The magnitude and relative sign of the two dipole moment components of NH2D are determined and previously measured nitrogen hyperfine structure for both species is reexamined using improved rotational wavefunctions.
The line widths, pressure-induced shifts, and center frequency of the J = 1-0, K = 0 phosphine transition at 266.9 GHz have been determined. The widths and shifts are reported for collisions with phosphine, H2, and He.
The temperature and pressure dependence of linewidths for the J = 11/2 - 9/2 and J = 15/2 - 13/2 transitions of ClO are determined by microwave spectroscopy. It is found that the widths for both transitions are the same within experimental error. The width parameter for nitrogen broadening is shown to be 3.35 + or - 0.17 MHz/torr at 317 K and 4.44 + or - 0.23 MHz/torr at 218 K.
The pressure broadening of oxygen transitions at 119 and 425 GHz have been measured in the laboratory for nitrogen and oxygen broadening as a function of temperature. The measured values are significantly different from estimates used by Woody and Richards to obtain a secondary calibration in their cosmic background measurements. The effect of the new determination is to move the calibrated cosmic background further from a Planck function.
Observations and assignments of some of the absorption lines in methanol from 200 to 850 GHz are reported. A simple phenomenological model is described which allows interpretation of spectra and prediction of new lines with little computational effort.
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A brief summary is presented of user requirements for the Shuttle synthetic aperture radar (SAR) to be flown on a sortie mission of 7 to 10 days in duration, based on information collected from survey of the literature and direct user contacts. This information suggests selection of a dual frequency (L and X band) dual polarization SAR capable of meeting most user requirements. Particular attention is given to the SAR system specifications and the data handling capability expected to be available during the 1980s for the tracking and data relay satellite system (TDRSS). The data link requirements of the majority of Shuttle experiments will eventually determine whether the necessary high-capacity Shuttle-TDRSS return link will be part of the intrinsic Shuttle capability or will be part of the SAR payload.
Preliminary proton nuclear magnetic resonance (NMR) studies were made to determine the applicability of this technique for the study of interactions between monomeric and polymeric amino acids with monomeric nucleic acid bases and nucleotides. Proton NMR results for aqueous solutions (D2O) demonstrated interactions between the bases cytosine and adenine and acidic and aromatic amino acids. Solutions of 5'-AMP admixed with amino acids exhibited more complex behavior but stacking between aromatic rings and destacking at high amino acids concentration was evident. The multisite nature of 5'-AMP was pointed out. Chemical shift changes for adenine and 5'-AMP with three water soluble polypeptides demonstrated that significant interactions exist. It was found that the linewidth-pH profile of each amino acid is unique. It is concluded that NMR techniques can give significant and quantitative data on the association of amino acid and nucleic acid constituents.
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