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355. The UV photochemistry of C2N2

Author

Halpern, Joshua B and Barts, Samuel A

Subjects
Atomic And Molecular Physics
Abstract

The absorption, emission, and photodissociation yield spectra of C2N2 were measured in the 220 and 210 nm region near the 4(0)1 and 1(0)1 4(0)1 bands of the A 1 sigma + from the X 1 sigma + system. The emission spectrum showed very few lines which appeared in the absorption spectrum. Moreover, the emission had 660 ns lifetime and, at 210 nm a very large electronic emission quenching rate. Laser induced fluorescence was used to measure the relative yield of CN radicals as a function of photolysis wavelength. This spectrum seemed to follow the absorption spectrum below the dissociation threshold. Energy in the CN fragments appeared to be statistically distributed.

Published
1989

356. The photochemistry of some possible cometary CN parent species

Author

Halpern, Joshua B

Subjects
Lunar And Planetary Exploration
Abstract

Laboratory work on the photochemistry of HC3N, C4N2, and CH3CN in relation to their possible role as CN parent molecules in comets is discussed. Photodissociation of HC3N, photolysis of C4N2, and quantum yields of excited CN(B) and CN(A) radicals from the VUV photolysis of CH3CN are considered.

Published
1987

362. Near-Resonant Two-Photon Excitation of CN.

Author

ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD, Guthrie, John A., Anderson, William R., Kotlar, Anthony J., Huang, Yuhui, Halpern, Joshua B., ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD, Guthrie, John A., Anderson, William R., Kotlar, Anthony J., Huang, Yuhui, and Halpern, Joshua B.

Abstract

Development of sensitive detection methods for CN is important because of applications to propellant flames. This radical plays a critical role in propellant combustion chemistry. We have observed a strong two photon absorption in the (3,0) band of CN by means of a resonant enhancement. Many lines are seen in the two photon spectrum due to multiple single photon near resonances in the (4,0) band. The detuning of the laser from these resonances varies from less than one to hundreds of wavenumbers, producing unusually large peak intensity variations in the two photon spectrum. This effect is not observed in two photon transitions far from resonance. Resonant enhancement is observed over a range from N = 5 to 20. We know of no other molecular two photon transition in which a near resonance produces such dramatically varying intensities over a short range of rotational levels. A calculation of the line strengths for these transitions reproduces the major features of the spectrum.

Published
1997

368. Parity-DependentRotational Energy Transfer in CN(A2Π, ν = 4, jF1ε) + N2, O2, and CO2Collisions.

Author

McGurk, Stephen J., Halpern, Joshua B., McKendrick, Kenneth G., and Costen, Matthew L.

Subjects
*ENERGY transfer, *PHOTOLYSIS (Chemistry), *CROSS-sectional method, *CARBON dioxide, *NITROGEN
Abstract

Wereport state-resolved total removal cross sections and state-to-staterotational energy transfer (RET) cross sections for collisions ofCN(A2Π, ν = 4, jF1ε) withN2, O2, and CO2. CN(X2Σ+) was produced by 266 nm photolysis of ICN ina thermal bath (296 K) of the collider gas. A circularly polarizedpulse from a dye laser prepared CN(A2Π, ν =4) in a range of F1erotationalstates, j= 2.5, 3.5, 6.5, 11.5, 13.5, and 18.5.These prepared states were monitored using the circularly polarizedoutput of an external cavity diode laser by frequency-modulated (FM)spectroscopy on the CN(A–X)(4,2) band. The FM Doppler profileswere analyzed as a function of pump–probe delay to determinethe time dependence of the population of the initially prepared states.Kinetic analysis of the resulting time dependences was used to determinetotal removal cross sections from the initially prepared levels. Inaddition, a range of j′ F1eand j′ F2fproduct states resultingfrom rotational energy transfer out of the j= 6.5 F1einitial state were probed,from which state-to-state RET cross sections were measured. The totalremoval cross sections lie in the order CO2> N2> O2, with evidence for substantial cross sectionsforelectronic and/or reactive quenching of CN(A, ν = 4) to unobservedproducts with CO2and O2. This is supportedby the magnitude of the state-to-state RET cross sections, where adeficit of transferred population is apparent for CO2andO2. A strong propensity for conservation of rotationalparity in RET is observed for all three colliders. Spin–orbit-changingcross sections are approximately half of those of the respective conservingcross sections. These results are in marked disagreement with previousexperimental observations with N2as a collider but arein good agreement with quantum scattering calculations from the samestudy (Khachatrianet al. J. Phys. Chem. A2009, 113, 3922). Our resultswith CO2as a collider are similarly in strong disagreementwith a related experimental study (Khachatrianet al. J. Phys.Chem. A2009, 113, 13390). We therefore propose that the previous experimentssubstantially underestimated the spin–orbit-changing crosssections for collisions with both N2and CO2, suggesting that even approximate quantum scattering calculationsmay be more successful for such molecule–molecule systems thanwas previously concluded. [ABSTRACT FROM AUTHOR]

Published
2014
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372. Laser Assisted CVD Growth of A1N and GaN

Author

HOWARD UNIV WASHINGTON DC DEPT OF CHEMISTRY, Halpern, Joshua B., Frye, Joan M., HOWARD UNIV WASHINGTON DC DEPT OF CHEMISTRY, Halpern, Joshua B., and Frye, Joan M.

Abstract

This is the final report of a project for investigating laser (assisted) methods of growing nitrile thin films. We have grown thin films of AlN and SiN by laser ablation from powders. We have also developed an efficient method for laser assisted CVD of aluminum, or aluminum containing films from trimethylalaminum.

Published
1993

374. Laser Assisted CVD Growth of A1N and GaN

Author

HOWARD UNIV WASHINGTON DC, Halpern, Joshua B., Frye, Joan M., Harris, Gary, Aluko, M., HOWARD UNIV WASHINGTON DC, Halpern, Joshua B., Frye, Joan M., Harris, Gary, and Aluko, M.

Abstract

This is the second annual report of a project for investigating the laser induced CVD growth of AIN and Gallium Nitrogen. In the second year significant progress has been made in the growth of AIN. AIN films have been produced by laser ablation. A new LI CVD source for A1 atoms has been characterized and verified by growth of A1 films. Additionally, some progress has been made in the understanding and characterization of alkyl aluminum-amino adducts which may be used for the growth of AIN. The goal of this project is to design, test and verify advanced laser induced chemical vapor deposition processes (LI-CVD), specifically for the growth of AlN. In the past year we have made progress in three areas: (a) Rapid growth of AlN thin films by laser ablation of AlN powders. (b) Demonstration of an advanced LI-CVD method for deposition of Al from trimethylaluminum (TMA1). This method was designed to be used as the aluminum atom source in AlN growth, but also has utility for laser deposition of aluminum interconnects, an area of current interest. (c) Synthesis and characterization of a number of stable alkyl aluminum-nitrogen containing adducts for future use in film growth. We have grown Alkylaluminum nitrogen thin films by laser ablation of powdered Alkylaluminum nitrogen compressed into a pellet.

Published
1991

378. Laser Assisted CVD Growth of A1N and GaN

Author

HOWARD UNIV WASHINGTON DC, Halpern, Joshua B., Frye, Joan M., Harris, Gary, Aluko, M., HOWARD UNIV WASHINGTON DC, Halpern, Joshua B., Frye, Joan M., Harris, Gary, and Aluko, M.

Abstract

This is the first annual report of a project for investigating laser assisted CVD growth of A1N and GaN. In the first year three experimental systems have been built. The first is a small, mobile CVD test system for evaluating growth schemes and detection methods for gas and heterogeneous phases. The second is a tunable diode laser spectrometer for monitoring gas phase components in a CVD reactor. The third is a dye laser system for monitoring atoms and small free radicals in the CVD system. First experiments have been done with all three systems. In particular we are investigating the use of 248 nm photolysis of trimethylalluminum near a slightly heated substrates in a mixture of TMA1 and hydrazine for growth of A1N.

Published
1990

379. Association of the minimal cyclophosphamide equivalent dose and outcome of microdissection testicular sperm extraction in patients with persistent azoospermia after chemotherapy

Author

Huang, I-Shen, Fantus, Richard J., Halpern, Joshua A., Wren, James, Bennett, Nelson E., Pham, Minh Nguyen, Stanisic, Alexander, Huang, William J., and Brannigan, Robert E.

Abstract

To investigate whether the minimal cyclophosphamide equivalent dose (mCED), a novel approach for estimating alkylating agent exposure, is associated with the sperm retrieval rates by microdissection testicular sperm extraction (mTESE) in azoospermic postchemotherapy cancer survivors.

Published
2023
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385. Poor survival of black patients in carcinoma of the endometrium

Author

Aziz, Hassan, primary, Rotman, Marvin, additional, Hussain, Fazal, additional, Smith, Glenda, additional, Chan, Eva, additional, Choi, Kwang, additional, Sohn, Chul, additional, Halpern, Joshua, additional, Schwartz, David, additional, Aral, Isamettin, additional, Fruchter, Rachel, additional, and Serur, Eli, additional

Published
1993
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395. COMMENT ON "FALSIFICATION OF THE ATMOSPHERIC CO2 GREENHOUSE EFFECTS WITHIN THE FRAME OF PHYSICS".

Author

HALPERN, JOSHUA B., COLOSE, CHRISTOPHER M., HO-STUART, CHRIS, SHORE, JOEL D., SMITH, ARTHUR P., and ZIMMERMANN, JÖRG

Subjects
*GREENHOUSE gases, *TRACE gases, *HEAT transfer, *ELECTROMAGNETIC waves, *GLOBAL warming, *CARBON dioxide
Abstract

In this journal, Gerhard Gerlich and Ralf D. Tscheuschner claim to have falsified the existence of an atmospheric greenhouse effect.1 Here, we show that their methods, logic, and conclusions are in error. Their most significant errors include trying to apply the Clausius statement of the Second Law of Thermodynamics to only one side of a heat transfer process rather than the entire process, and systematically ignoring most non-radiative heat flows applicable to the Earth's surface and atmosphere. They claim that radiative heat transfer from a colder atmosphere to a warmer surface is forbidden, ignoring the larger transfer in the other direction which makes the complete process allowed. Further, by ignoring heat capacity and non-radiative heat flows, they claim that radiative balance requires that the surface cool by 100 K or more at night, an obvious absurdity induced by an unphysical assumption. This comment concentrates on these two major points, while also taking note of some of Gerlich and Tscheuschner's other errors and misunderstandings. [ABSTRACT FROM AUTHOR]

Published
2010
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