Browsing by Author "Lee, L. C."

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Absorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 140-220 nm and implications for planetary isotopic fractionation
(2006-08-20)
Cheng, Bing-Ming
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Lu, Hsiao-Chi
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Chen, Hong-Kai
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Bahou, Mohammed
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Lee, Yuan-Pern
Cross sections for photoabsorption of NH3, NH2D, NHD2, and ND3 in the spectral region 140-220 nm were determined at similar to 298 K using synchrotron radiation. Absorption spectra of NH2D and NHD2 were deduced from spectra of mixtures of NH3 and ND3, of which the equilibrium concentrations for all four isotopologues obey statistical distributions. Cross sections of NH2D, NHD2, and ND3 are new. Oscillator strengths, an integration of absorption cross sections over the spectral lines, for both A X and B X systems of NH3 agree satisfactorily with previous reports; values for NH2D, NHD2, and ND3 agree with quantum chemical predictions. The photolysis of NH3 provides a major source of reactive hydrogen in the lower stratosphere and upper troposphere of giant planets such as Jupiter. Incorporating the measured photoabsorption cross sections of NH3 and NH2D into the Caltech/JPL photochemical diffusive model for the atmosphere of Jupiter, we find that the photolysis efficiency of NH2D is lower than that of NH3 by as much as 30%. The D/H ratio in NH2D/NH3 for tracing the microphysics in the troposphere of Jupiter is also discussed.
Autoionizing Rydberg series (np ', nf ') of Ar investigated by stepwise excitations with lasers and synchrotron radiation
(2008-08-01)
Lee, Yin-Yu
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Dung, Tzan-Yi
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Hsieh, Re-Ming
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Yuh, Jih-Young
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Song, Yen-Fang
Synchrotron radiation is used to excite Ar to the intermediate states 3p(1/2)(5) (3d '[3/2](1), 5d '[3/2](1), 5s '[1/2](1,) 7s '[1/2](1)) and 3p(3/2)(5) (6d[1/2](1), 6d[3/2](1), 8s[3/2](1)), then excited by lasers to the autoionizing Rydberg series 3p(1/2)(5) np ' ([1/2](0,1), [3/2](1,2)) and nf '[5/2](2). For the intermediate states of 5s ', 7s ', and 8s, the np ' ([1/2](0) and [3/2](2)) series are observed with high intensity but not the np ' ([1/2](1) and [3/2](1)) series when the polarization vectors of two light beams are in parallel; but when they are in orthogonal, the np '[1/2](0) series disappears, the np '[3/2](2) intensity remains, and the np ' ([1/2](1) and [3/2](1)) series show up strongly. The intensity distribution of the np ' series strongly depends on the intermediate state. The spectra of the np ' series are assigned according to their intensity variation with the polarization vectors. The quantum defects determined for the series np '[1/2](0)(n=11-57), np '[312](2)(n=11-65), np '[3/2](1)(n=11-31), and nf '[5/2](2)(n=9-74) are 1.611 +/- 0.011, 1.683 +/- 0.013, 1.688 +/- 0.010, and 0.016 +/- 0.005, respectively. Our values are in excellent agreement with theoretical prediction. The spectral line shapes of autoionizing Rydberg states are analyzed with a Beutler-Fano profile. Reduced autoionization linewidths for the np '[1/2](0)(n= 11-16) series vary in the range 2549-4145 cm(-1), and the nf '[5/2](2)(n=9-11) series in 186-247 cm(-1) in reasonable agreement with theoretical prediction.
Electrical characteristics of Ni Ohmic contact on n-type GeSn
(2014-06-16)
Li, H.
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Cheng, H. H.
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Lee, L. C.
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Lee, C. P.
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Su, L. H.
We report an investigation of the electrical and material characteristics of Ni on an n-type GeSn film under thermal annealing. The current-voltage traces measured with the transmission line method are linear for a wide range of annealing temperatures. The specific contact resistivity was found to decrease with increasing annealing temperature, followed by an increase as the annealing temperature further increased, with a minimum value at an annealing temperature of 350 degrees C. The material characteristics at the interface layer were measured by energy-dispersive spectrometer, showing that an atomic ratio of (Ni)/(GeSn) = 1:1 yields the lowest specific contact resistivity. (C) 2014 AIP Publishing LLC.
Kinetics and Mechanism of the NCN+NO2 Reaction Studied by Experiment and Theory
(2008-10-16)
Yang, Tsung-Ju
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Wang, Niann S.
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Lee, L. C.
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Xu, Z. F.
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Lin, M. C.
The rate constant for the NCN + NO2 reaction has been measured by a laser photolysis/laser-induced fluorescence technique in the temperature range of 260-296 K at pressures between 100 and 500 Torr with He and N-2 as buffer gases. The NCN radical was produced from the photolysis of NCN3 at 193 nm and monitored by laser-induced fluorescence with a dye laser at 329.01 nm. The rate constant was found to increase with pressure but decrease with temperature, indicating that the reaction occurs via a long-lived intermediate stabilized by collisions with buffer gas. The reaction mechanism and rate constant are also theoretically predicted for the temperature range of 200-2000 K and the He and N-2 pressure range of 10(-4) Torr to 1000 atm based on dual-channel Rice-Ramsperger-Kassel-Marcus (RRKM) theory with the potential energy surface evaluated at the G2M//B3LYP/6-311+G(d) level. In the low-temperature range (< 700 K), the most favorable reaction is the barrierless association channel that leads to the intermediate complex (NCN-NO2). At high temperature, the direct O-abstraction reaction with a barrier of 9.8 kcal/mol becomes the dominant channel. The rate constant calculated by RRKM theory agrees reasonably well with experimental data.
Photoabsorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 110-144 nm
(2007-10-21)
Wu, Yu-Jong
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Lu, Hsiao-Chi
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Chen, Hong-Kai
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Cheng, Bing-Ming
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Lee, Yuan-Pern
Cross sections for photoabsorption of NH3, NH2D, NHD2, and ND3 near 298 K were measured in the spectral range of 110-144 nm using radiation from a synchrotron. Absorption cross sections and oscillator strengths of NH3 agree satisfactorily with previous reports; those of ND3 are improved over those in a previous report, whereas those of NH2D and NHD2 are new. The oscillator strengths of transitions to D, D-', D-'', F, and G states are nearly the same among all four isotopic variants, but those to D-''' and E states vary substantially. Observed absorption bands are arranged into vibrational progressions in accord with known Rydberg transitions. All progressions show a common trend of vibrational intervals increasing with vibrational quantum numbers. The Rydberg orbitals for states D(3de('')), D-'(4sa(1)(')), D-''(3da(1)(')), D-'''(4pe(')), and E(4de('')) are readily assigned with quantum defects determined in these experiments, but assignments for F(5de('')) and G(6de('')) are uncertain. Absorption cross sections of dissociative continua underneath discrete structures are larger for NH2D and NHD2 than for NH3 and ND3, indicating that the rate of dissociation of ammonia might increase when its symmetry is broken. (C) 2007 American Institute of Physics.