Engineering topics

Pine, A. S.

Publications and source records attributed to Pine, A. S..

11 records

NASA NTRS1993

Spectral intensities in the nu(sub 1) band of NH3

Intensities have been measured for individual transitions in the Q and R branches of the nu(sub 1) band of NH3 using a difference-frequency laser spectrometer. The data yield an integrated band strength of S(sup 0 sub v) = 219.36 +/- 1.03/sq cm/MPa at 297 K, corresponding to a transition moment of absolute value of mu(sub v) = 8.535(20) x 10(exp -32) C x m, and a Herman-Wallis correction factor,(1 + alpha(sub J)m), where alpha(sub J) = 0.0209(20). The intensities of a few lines for K greater than or equal to 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2nu(sub 4)(E, l = 2), so were excluded from the fit. A small sample of nu(sub 3) band lines occurring in the nu(sub 1) band scans also yields a rough estimate of the nu(sub 3) band intensity with evident irregular perturbations.

Pine, A. S.↗

NASA NTRS1993

Molecular-beam spectrum of the 970/cm Fermi triad of CF3CH3

A tunable MW-sideband CO2 laser is used with an electric-resonance optothermal spectrometer to investigate the IR spectrum of CF3CH3 near 970/cm. A Fermi-coupled triad of states is observed, resulting from the interactions of 2nu6+nu11 and nu5+nu12 with the fundamental vibration, nu10, which is assumed to carry the oscillator strength in this region. The high resolution (about 3 MHz) of the spectrometer allows the observation of tunneling splittings associated with the nu6 torsional vibration. These splittings are used to identify the torsional character of the states observed. At the normal-mode level the nu10 and nu5+nu12 states are found to be nearly degenerate and interacting by an anharmonic matrix element of about 3/cm. The present investigation illustrates the utility of using resolved torsional splittings to unravel complex vibrational couplings in molecules.

Fraser, G. T.↗

NASA NTRS1993

Self-, N2- and Ar-broadening and line mixing in HCN and C2H2

Self-, N2- and Ar-broadening coefficients were measured for the stretch-bend infrared combination bands nu-1 + nu-1/2 (4004/cm) of HCN and nu-1 + nu-1/5 (4091/cm) of C2H2, using a tunable difference-frequency laser. At atmospheric pressures, the Q branches of these bands exhibit significant rotational narrowing or line mixing. The broadening coefficients are fit with empirical rotationally inelastic collision rate laws, which are then used to model the line mixing in the overlapped Q-branch profiles. Simple energy gap fitting laws appear to be suitable for the shorter-range intermolecular quadrupole-quadrupole and induction forces, whereas an energy-corrected-sudden scaling law works better for the longer-range dipole-dipole and dipole-quadrupole collision partners. In all cases, the line-coupling coefficients are substantially reduced from the rotationally inelastic rates fit to the broadening coefficients, indicating that 35-70 percent of the broadening may be due to other collisional mechanisms such as cross-relaxation to the degenerate H state vibrational level.

Pine, A. S.↗

NASA NTRS1993

Self broadening in the nu-1 band of NH3

Self-broadening coefficients, pressure shifts, and integrated intensities have been measured for Q- and R-branch transitions in the nu-1 fundamental band of ammonia using a difference-frequency laser spectrometer. A strong, systematic J and K dependence of the broadening coefficients, reminiscent of the ground-state inversion transitions, is observed and compared with semiclassical line broadening calculations. Dicke narrowing is evident at intermediate pressures for the sharpest lines, primarily the R(J, 0) transitions. Incipient line mixing is apparent in the Q branch at pressures above about 0.1 bar.

Markov, V. N.↗

NASA NTRS1992

Polarization-stabilized 1.15- and 3.39-micron He-Ne lasers

Two methods for polarization stabilization of an internal-mirror 3.39-micron He-Ne laser are reported. The first relies on a concurrently lasing 1.15-micron transition by fixing the relative amplitude of two orthogonally polarized longitudinal modes that are split by a Rochon prism and detected with separate Si photodiodes. In the second method, two spatially separated orthogonally polarized adjacent 3.39-micron modes are optically balanced, differentially chopped, and recombined on a single InSb photodiode for phase-sensitive detection. The dual-wavelength scheme has been tested by beating against a methane-stabilized 3.39-micron He-Ne laser, which yields maximum excursions of less than 0.5 MHz over several hours and comparable reproducibility. The polarization-stabilized He-Ne laser has been used as a reference for a tunable color-center laser molecular-beam optothermal spectrometer and provides a precision of better than 2 MHz.

Junttila, M.-L.↗

NASA NTRS1992

Self-, N2, O2, H2, Ar, and He broadening in the nu3 band Q branch of CH4

Self-, N2-, O2-, H2-, Ar-, and He-broadening coefficients, pressure shifts, and integrated intensities have been measured for most transitions in the Q branch of the nu3 fundamental band of methane using a difference-frequency laser spectrometer. A systematic dependence of the broadening coefficients on the tetrahedral symmetry species and order index is observed with striking similarities for N2, O2, and Ar and for H2 and He buffer gases. Comparison with earlier measurements on other bands and branches of methane indicates very little vibrational, branch, or carbon isotope dependence. Dicke narrowing is evident at intermediate pressures, yielding an average narrowing coefficient and an optical diffusion constant for each gas mixture.

Pine, A. S.↗

NASA NTRS1992

Self-broadening and line mixing in HCN Q branches

A tunable difference-frequency laser has been used to record Q-branch spectra of the nu sub 1 + nu sub 2 (4004/cm) and nu sub 2 + nu sub 3 (2806/cm) combination bands, as well as the nu sub 1 - nu sub 2 (2599/cm) difference hot band of HCN, at 1-400 torr pressures. Line mixing is noted in the strongly overlapped, higher-pressure Q-branch profiles from the nonradiative Lorentzian superposition of the component transitions. An effective R to T transition energy-corrected-sudden scaling law is found to give a consistent and satisfactory fit to the Q-branch profiles of all three bands.

Pine, A. S.↗

NASA NTRS1990

Decoupling in the line mixing of acetylene infrared Q branches

A difference-frequency laser spectrometer was used to record the Q-branch profiles of the nu1 + nu5, nu3 + nu4, and nu2 + 2nu4 + nu5 Pi(u)-Sigma(g) combination bands in the 2.5 micron C-H stretch-bend region of acetylene. The experiment was carried out at pressures in the range of 1 to 500 Torr. It is shown that line mixing causes substantial deviation of collisionally overlapped Q-branch profiles from the independently additive superposition of Lorentzian line shapes. It is also found that the degree of line mixing is greatly reduced from that assuming all the broadening arises from rotationally inelastic collisions coupling Q-branch lines only to one another.

Pine, A. S.↗

NASA NTRS1990

Infrared spectra of van de Waals complexes of importance in planetary atmospheres

It has been suggested that (CO2)2 and Ar-CO2 are important constituents of the planetary atmospheres of Venus and Mars. Recent results on the laboratory spectroscopy of CO2 containing van der Waals complexes which may be of use in the modeling of the spectra of planetary atmospheres are presented. Sub-Doppler infrared spectra were obtained for (CO2)2, (CO2)3, and rare-gas-CO2 complexes in the vicinity of the CO2 Fermi diad at 2.7 micrometers using a color-center-laser optothermal spectrometer. From the spectroscopic constants the geometries of the complexes have been determined and van der Waals vibrational frequencies have been estimated. The equilibrium configurations are C2h, C3h, and C2v, for (CO2)2, (CO2)3, and the rare-gas-CO2 complexes, respectively. Most of the homogeneous linewidths for the revibrational transitions range from 0.5 to 22 MHz, indicating that predissociation is as much as four orders of magnitude faster than radiative processes for vibrational relaxation in these complexes.

Fraser, G. T.↗

NASA NTRS1989

Photoacoustic measurement of differential broadening of the Lambda doublets in NO(X 2Pi 1/2,v = 2-0) by Ar

A differential broadening of the Lambda doublets in the v = 2-0 overtone band of the 2pi1/2 ground electronic state of NO in an Ar buffer gas has been observed by photoacoustic spectroscopy using a tunable color-center laser. The broadening coefficients for the f symmetry components are larger than for the e symmetry components by up to about 6 percent for J of about 16.5. This differential depends on J and vanishes at low J, implicating the anisotropy of the unpaired electron Pi orbital in the plane of rotation. The 2Pi3/2 transitions are slightly broader than the 2Pi1/2 as a result of spin-flipping collisional relaxation. The observed line shapes also exhibit collisional or Dicke narrowing due to velocity-changing collisions.

Pine, A. S.↗

NASA NTRS1967

Electron and solid state physics

Electron and solid state physics - reflected light, Raman effects, solid and liquid optical properties, spectroscopy, Brillouin effects, and carbon dioxide laser

BRILLOUIN EFFECT↗