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At least 145 records · Page 8
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NASA NTRS1991

Molecular hydrogen formation by excited atom radiative association

The results from a semiclassical calculation of the thermal rate coefficient for the radiative association process H(n = 2) + H(n = 1) - H2 + hv are presented (n is the principal quantum number of the separated hydrogen atoms). The relative importance of this reaction in various environments is briefly discussed. Models of the early universe around the epoch of recombination and protostellar winds have been calculated which include the excited atom process. Not surprisingly, it is shown that the excited atom process will not be important in the general interstellar medium, except possibly in environments where the amount of Ly-alpha photon trapping is large. Examples may be the material surrounding quasars, active galactic nuclei, and bright H II regions. The most likely application of this process might be within rapidly evolving systems where a large transient n = 2 population of neutral hydrogen could result in a burst of molecular hydrogen formation.

Latter, William B.↗
NASA NTRS1991

Rotational and vibrational effects in the E 1Sigma(+)g-X 1Sigma(+)g two-photon transitions of H2, HD, and D2

This paper reports a theoretical study of the dependence of the E 1Sigma(+)g v(E) = 0, J-X 1Sigma(+)g, v(X),J transitions in H2, HD, and D2 on the initial vibrational and rotational quantum numbers v(X) and J. The results demonstrate the concerted nature of two-photon transitions. The magnitude of the two-photon transition moment increases with v(X) between 0 and 2, then decreases rapidly at higher v(X). The J dependence of the two-photon transition moment is most strongly affected by the changes in vibrational wave functions caused by centrifugal distortion of the vibrational potential. It is shown that the J variation can be used as a probe of resonant tunneling in the double-well potential of the E,F state.

Huo, Winifred M.↗
NASA NTRS1991

Effect of the rotational-vibrational excitation on molecular diameters

The kinetic molecular diameters of rotationally and vibrationally excited diatomic molecules and molecular ions are derived as functions of the rotational and vibrational quantum numbers of the molecules. Typical molecular diameters are studied in two cases: in low-temperature gas, where the molecular diameter is independent of the degree of rotational-vibrational excitation of the molecules, and in high-temperature gas, where the molecular diameter depends on the degree of rotational-vibrational excitation of the molecules. The rotational-vibrational excitation of molecules is shown to have a meaningful effect on the collisional properties of gases. The effect is stronger in gases of weakly-bound molecules.

Kang, S. H.↗
NASA NTRS1991

Anomalous gain in an isotopically mixed CO2 laser and application to absolute wavelength calibration

Measurements are reported on a grating-tuned CO2 laser, containing an isotropic mixture of O-16C-12O-16, O-16C-12O-18, and O-18C-12O-18. The P6 and R14 lines of O-16C-12O-16 were found to have anomalously high intensities. These anomalies are produced by the near coincidence of the transition frequencies in two distinct isotopes, permitting them to act as a single indistinguishable population. These two lines can be used to identify the rotational quantum numbers in the P and R branch spectra, thereby permitting absolute wavelength calibration to be achieved.

Hewagama, Tilak↗
NASA NTRS1991

Measurements of self-broadening of infrared absorption lines of ozone

Lorentz self-broadening coefficients have been determined for 355 spectral lines belonging to five different infrared vibration-rotation bands of O3 in the spectral region from 4.8 to 17 microns. Six ozone absorption spectra, recorded at room temperature using a Fourier transform spectrometer, were analyzed. The half-width values were obtained through a nonlinear least-squares spectral fitting procedure. The results are compared with previous measurements, and the vibration of the half-widths with vibrational and rotational quantum numbers is examined.

Smith, M. A. H.↗
NASA NTRS1991

Radiative widths and splitting of cyclotron lines in superstrong magnetic fields

The radiative line widths of the Landau levels in a superstrong magnetic field are calculated and simple analytic expressions and fits are given for these which are valid over a wide range of the principal quantum number and the magnetic field strength. If QED corrections are not taken into account, all levels but the first are doubly degenerate, corresponding to the two possible spin projections. However, the interaction with the QED vacuum removes this degeneracy, leading to an energy splitting of each level which exceeds the radiative linewidth for low Landau levels if the magnetic field is not too large (B is less than approximately 10 exp 13 G). Estimations are presented of the splitting in various limits as a function of field strength and Landau number. The possibility of observing this splitting in accreting X-ray pulsars and in gamma-ray bursters is discussed.

Pavlov, G. G.↗
NASA NTRS1991

Global analysis of fermion mixing with exotics

The limits are analyzed on deviation of the lepton and quark weak-couplings from their standard model values in a general class of models where the known fermions are allowed to mix with new heavy particles with exotic SU(2) x U(1) quantum number assignments (left-handed singlets or right-handed doublets). These mixings appear in many extensions of the electroweak theory such as models with mirror fermions, E(sub 6) models, etc. The results update previous analyses and improve considerably the existing bounds.

Nardi, Enrico↗
NASA NTRS1991

Heterodyne spectroscopy of carbon monoxide lines perturbed by hydrogen and helium

Infrared heterodyne spectroscopy has been used for the first time to measure the widths and shifts of CO rovibrational spectra perturbed by H2 and He. A spectral resolution of 20 MHz was achieved. The CO-He line-broadening measurements were accurate enough to distinguish between two proposed intermolecular potential models of this system. Also, a measured increase in the broadening coefficient as a function of rotational quantum number j was observed for CO-He at temperatures of 80 K. This is not easy to explain in the context of so-called 'sudden approximations' which have been used to interpret pressure broadening data for this system.

Mannucci, Anthony J.↗
NASA NTRS1991

Radiative transition probabilities for all vibrational levels in the X 1Sigma(+) state of HF

Recent analyses have led to an experimentally-based potential energy curve for the ground state of HF which includes nonadiabatic corrections and which joins smoothly to the long-range potential at an accurately determined dissociation limit. Using this potential curve and a new ab initio dipole moment function, accurate radiative transition probabilities among all vibrational levels of the ground state of HF have been calculated for selected rotational quantum numbers. Comparisons of Einstein A spontaneous emission coefficients, dipole moment absorption matrix elements, and Herman-Wallis factors for absorption bands are presented.

Zemke, Warren T.↗
NASA NTRS1991

Effect of nearest-neighbor ions on excited ionic states, emission spectra, and line profiles in hot and dense plasmas

The effect of the cylindrical symmetry imposed by the nearest-neighbor ions on the ionic levels and the emission spectra of a Li-like Kr ion immersed in hot and dense plasmas is investigated using the Stein et al. (1989) two-centered model extended to include computations of the line profiles, shifts, and widths, as well as the energy-level mixing and the forbidden transition probabilities. It is shown that the cylindrical symmetry mixes states with different orbital quantum numbers l, particularly for highly excited states, and, thereby, gives rise to forbidden transitions in the emission spectrum. Results are obtained for the variation of the ionic level shifts and mixing coefficients with the distance to the nearest neighbor. Also obtained are representative computed spectra that show the density effects on the spectral line profiles, shifts, and widths, and the forbidden components in the spectrum.

Salzmann, D.↗
NASA NTRS1989

A new analysis of the vibration-rotation spectrum of CH from solar spectra

In the solar spectrum, CH vibration-rotation lines are excited to higher vibrational and much higher rotational quantum numbers than in any laboratory source. Observations were made, for the first time, of a very large number of new lines (1-0 and 2-1 up to J = 34.5, 3-2 up to J = 31.5, and even 4-3, never seen before, up to J = 24.5) on solar spectra obtained from space, with the ATMOS-SL3 instrument. A total of 558 lines have been used to derive new accurate molecular constants for the X 2Pi ground state of CH.

Melen, F.↗
NASA NTRS1993

Rotational level-dependent collisional broadening and line shift of the A2Sigma(+)-X2Pi (1,0) band of OH in hydrogen-air combustion gases

Measurements of the collisional broadening and line shift of the (1,0) band of the A2Sigma(+)-X2Pi system of OH are reported in atmospheric pressure hydrogen-air combustion gases. The measurements were made using a single-mode, narrow linewidth, frequency-doubled ring dye laser operating near 283 nm. The OH was generated in the combustion gases of a flat flame H2-air burner. Collisional broadening parameters for equilibrium mixtures of H2, O2, H2O, and N2 were obtained spanning a range of fuel/air equivalence ratios from 0.6 to 1.6 and temperatures from 1500 to 2050 K. Measurements were obtained spanning rotational quantum numbers from 4.5 to 16.5. The collision induced frequency shift was determined to be 0.1 that of the collisional broadening.

Kessler, W. J.↗
NASA NTRS1993

Collisional excitation of CO by H2O - An astrophysicist's guide to obtaining rate constants from coherent anti-Stokes Raman line shape data

Rate constants for excitation of CO by collisions with H2O are needed to understand recent observations of comet spectra. These collision rates are closely related to spectral line shape parameters, especially those for Raman Q-branch spectra. Because such spectra have become quite important for thermometry applications, much effort has been invested in understanding this process. Although it is not generally possible to extract state-to-state rate constants directly from the data as there are too many unknowns, if the matrix of state-to-state rates can be expressed in terms of a rate-law model which depends only on rotational quantum numbers plus a few parameters, the parameters can be determined from the data; this has been done with some success for many systems, especially those relevant to combustion processes. Although such an analysis has not yet been done for CO-H2O, this system is expected to behave similarly to N2-H2O which has been well studies; modifications of parameters for the latter system are suggested which should provide a reasonable description of rate constants for the former.

Green, Sheldon↗
NASA NTRS1993

Rotational dependence of the predissociation linewidths of the Schumann-Runge bands of O2

The rotational coupling constant for the O2 molecule is estimated theoretically, and the predissociation linewidths of the Schumann-Runge bands of vibration levels v = 0-12 are calculated for (O-16)2, (O-16)(O-18), and (O-18)2 molecules in the B 3Sigma-u(-) state. Calculations accounted for both the spin-orbit and rotational couplings with rotational quantum number N up to 20. The theoretical linewidths are compared with experimental widths, showing satisfactory agreement.

Cheung, A. S.-C.↗
NASA NTRS1992

Submillimeter, millimeter, and microwave spectral line catalogue, revision 3

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.

Pickett, H. M.↗
NASA NTRS1995

Coherent state constructions of bases for some physically relevant group chains

Rotor coherent state constructions are given for the Wigner supermultiplet SU(4) contains SU(2)xSU(2) and for the special irreducible representations (N0) of the SO(5) contains SO(3) contains SO(2) group chain in exact parallel with the rotor coherent state construction for the SU(3) contains SO(3) contains SO(2) case given by Rowe, LeBlanc,, and Repka. Matrix elements of the coherent state realizations of the group generators are given in all cases by very simple expressions in terms of angular momentum Wigner coefficients involving intrinsic projection labels K. The K-matrix technique of vector coherent state theory is used to effectively elevate these K labels to the status of good quantum numbers. Analytic expressions are given for the (K K*)-matrices for many of the more important irreducible representations.

Hecht, Karl T.↗
NASA NTRS1994

Rovibrational intensities of the minor isotopes of the CO X (sup 1)Sigma (sup +) state for v less than or equal to 20 and J less than or equal to 150

Electric dipole transition matrix elements for rovibrational transitions in the X (sup 1)Sigma(sup +) state of the CO minor isotopes (14)C(16)O and (13)C(17)O are calculated for the first time for all the delta v = +1, +2, and +3 transitions for which v less than or equal to 20 and J less than or equal to 150. Improved electric dipole transition matrix elements are also calculated for the minor isotopes (12)C(17)O, (12)C(18)O, (13)C(18)O. We have fitted polynomials to these matrix elements as a function of the parameter m which is defined in terms of the lower state angular momentum quantum number J; the convenient to use polynomial representations are given in tabular form. These results for the minor species of CO complement those previously reported by us for (12)C(16)O and (13)C(16)O.

Goorvitch, D.↗
NASA NTRS1994

Calculation of (12)C(16)O and (13)C(16)O X(1)Sigma(+) rovibrational intensities for v less than or equal to 20 and J less than or equal to 150

Improved electric dipole transition matrix elements for rovibrational transitions in the ground state X(1)Sigma(+) of (12)C(6)O and (13)C(16)O are calculated for all the delta v = +1, +2, and +3 transitions for which v less than or equal to 20 and J less than or equal to 150. We have fitted polynomials to these matrix elements as a function of the parameter m which is defined in terms of the lower state angular momentum quantum number J. These convenient to use polynomial representations are given in Tables 1-4 for (12)C(16)O and in Tables 5-8 for (13)C(16)O. We observe that there is intensity enhancement due to vibration-rotation interaction for the P-branch transitions at the expense of the R-branch transitions for delta v = +1. This enhancement can be as large as 40% at the highest J. For the delta v = +2 and +3 transitions, the R-branch transitions are enhanced by as much as a factor of 2.75 and 10 at the highest J, respectively. The P-branch transitions exhibit only minor decreases. Comparisons with previous calculations show good agreement for the delta v = +1 transitions. The comparison for delta v = +2 and +3 transitions show differences as large as a factor of 5.

Goorvitch, D.↗