Short-wavelength Photons Research Articles

On the Relationship between Radiative Entropy and Temperature Distributions

Abstract The Earth can be viewed as a complex nonequilibrium system that exchanges primarily radiative energy and entropy with its surroundings. The energy balance equation provides an important constraint on the distribution of outgoing radiation since the net global energy exchange will be close to zero over some appropriately long time interval. The entropy of the radiation does not obey such a conservation law, instead the outgoing entropy irradiance is much greater than the incoming amount. Most of this increase in the entropy flux is due to the conversion of short wavelength photons from a small solid angle into longer wavelength photons that are emitted nearly isotropically. If the entropy irradiance is calculated with sufficient precision, it is possible to relate it to the distribution of radiative temperature over position, direction, wavenumber and polarization spaces. The radiative entropy decreases as the variance of the radiative temperature distribution increases over any of the four spaces...

ChemInform Abstract: Stereoselective Photooxidation of trans‐2‐Butene to Epoxide by Nitrogen Dioxide Excited with Red Light in a Cryogenic Matrix.

Reaction was induced between trans-2-butene and nitrogen dioxide by exciting trans-2-butene-NO{sub 2} pairs, isolated in solid Ar at red, yellow, and green wavelengths (NO{sub 2}{sup 2}B{sub 2} {l arrow} {anti X}{sup 2}A{sub 1}). The chemistry was monitored by FT-infrared spectroscopy, and Ar ion and cw dye lasers were used for photolysis. Products formed were 2-butene oxide + NO, the former under complete retention of stereochemistry, and an addition product that was identified by {sup 18}O isotopic substitution as a butyl nitrite radical, reported here for the first time. Analysis of the photolysis-wavelength dependence of the butyl nitrite radical and trans-2-butene oxide (NO) growth kinetics revealed that epoxide + NO is formed along two reaction pathways. The first gives trans-2-butene oxide + NO and butyl nitrite radical upon absorption of a single photon by trans-2-butene-NO{sub 2} pairs (one-photon path). The second path is formation of trans-2-butene oxide + NO by photodissociation of trapped butyl nitrite radical by a (second) red or shorter wavelength photon (two-photon path). Two alternative transients are proposed for the one-photon path, namely a hot butyl nitrite radical and an oxirane biradical, respectively. The wavelength dependence of the product branching along the one-photon path indicates that branching occursmore » from a vibrationally unrelaxed transient. This suggests that the observed stereochemical integrity originates from insufficient coupling of the stretching and bending vibrations of the transient with torsion around its central C-C bond on the time scale of reaction to epoxide + NO and its stabilization as butyl nitrite radical.« less

Hydrogenated amorphous carbon grains in reflection nebulae

view Abstract Citations (99) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrogenated Amorphous Carbon Grains in Reflection Nebulae Witt, Adolf N. ; Schild, Rudolph E. Abstract The paper presents spectroscopic data which identify the source of the photometrically detected extended red emission in the reflection nebulae NGC 2023 and NGC 7023 as emission in the form of a broad luminescence band, reaching its peak in the 6600-6800 A wavelength region. This feature is identified as luminescence from hydrogenated amorphous carbon, excited by short-wavelength photons from the central illuminating stars. In NGC 2023 the luminescence is found to be notably enhanced in a filamentary shell structure surrounding HD 39703, which is spatially coincident with a region exhibiting fluorescent molecular hydrogen emission as well as 3.3-micron emission. From BVRI surface photometry of NGC 2023 and NGC 7023 it is concluded that in regions of enhanced luminescence, presumably regions containing hot atomic hydrogen, the luminescence band shifts toward shorter wavelengths, while in more remote molecular regions more luminescent energy emerges in the long-wavelength tail of the band. This observed behavior is consistent with laboratory results concerning luminescence of hydrogenated amorphous carbon under varying conditions. Publication: The Astrophysical Journal Pub Date: February 1988 DOI: 10.1086/166054 Bibcode: 1988ApJ...325..837W Keywords: Amorphous Materials; Astronomical Spectroscopy; Carbon; Hydrocarbons; Interstellar Matter; Reflection Nebulae; Astronomical Photometry; H Alpha Line; Luminescence; Spectrum Analysis; Stellar Envelopes; Astrophysics; INTERSTELLAR: GRAINS; NEBULAE: REFLECTION full text sources ADS | data products SIMBAD (5)

Submicron lithography in Japan

Abstract1Mbit D‐RAM. the most advanced VLSI device, is realized by a high performance stepper with the conventional optical techniques. However, as the optical lithography has an inherent limit of resolution, new technologies are being developed rapidly for the development of new generation VLSI devices (4M‐16Mbit D‐RAM) using shorter wavelength photons of i‐line. Electron beam (EB) lithography is already in practical mask making products, but the resolution limit is about 0.5 μm because of proximity effects. In order to make higher resolution and higher precision masks, high voltage EB technique is being developed to minimize the proximity effect, and fabricated 0.25 μm line and space by a single scan at 50kV. X‐ray technology 1; becoming practical after a long laboratory‐level study, using high performance X‐ray resists (CPMS: chlorinated polymetylstylene). Focused Ion Beam (FIB) technology has been anticipated for its capability of submicron lithography due to a reduced proximity effect. High speed submicron Si MOSFET and GaAs MESFET with 0.25 μm gate have been fabricated using FIB technology. Activities of submicron lithography technology in Japan (optical stepper, EB, X‐ray, and FIB) are described.

Wavelength-Dependent Decay Times and Time-Dependent Spectra of the Singlet-Exciton Luminescence in Anthracene Crystals

Decay curves and spectral shapes of the singlet-exciton luminescence in anthracene crystals have been studied at room temperature and found to depend on the experimental geometry and on the penetration depth of the exciting light. The well-known wavelength-dependent decay time and time-dependent spectrum occur only when the luminescence is excited in the process of the one-photon absorption and is observed in the backward-scattering geometry. In the forward-scattering geometry, the decay time is independent of the luminescence wavelength. When the excitons are uniformly generated in the crystal in the process of the two-photon absorption, the wavelength-dependent decay time and time-dependent spectrum do not occur even in the backward-scattering geometry. These results are interpreted in terms of diffusion of the singlet excitons and reabsorption of the short wavelength photons of the exciton luminescence.

Wavelength dependence for AMT crosslinking of pBR322 DNA.

Abstract The wavelength dependence for 4′aminomethyl‐4,5′,8‐trimethylpsoralen crosslinking of a linearized plasmid DNA (pBR322) by narrow band UV‐A light (298–382 nm) has been determined. Maximal levels of crosslinking occurred with light in the 322–346 nm range. Crosslinks were shown to be photoreversible by shorter wavelength photons (298 and 310 nm). The correlation between the wavelength dependence for crosslink formation and the optimal wavelength for most psoralen action spectra further supports the notion that crosslinks are the major lesion responsible for the effectiveness of psoralen plus ultraviolet A therapies.

A new amorphous silicon camel diode

The dark current voltage characteristics, the wavelength dependence of photocurrents, and the photovoltaic properties of a-Si:H camel diodes have been investigated. The internal photoemission over the potential barrier in the bulk of the amorphous silicon and the internal gain of photocurrents at short wavelength photons have been observed.

Emission of short-wavelength photons from ion-surface charge exchange

The intensity of radiation emitted from ion-surface charge exchange processes can be significantly enhanced if the surface exposed to impinging ions is electronically excited. Alpha particles capturing electrons at a silicon surface are considered as possible candidates for a short-wavelength laser.

The motion of short-wavelength photons in gravitating, refractive media

view Abstract Citations (1) References (3) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The motion of short-wavelength photons in gravitating, refractive media Noonan, T. W. Abstract The field-to-particle derivation of a photon in a medium begun in an earlier paper is here extended to the case where the wavelength is short compared with variations in the electromagnetic properties of the medium. The equation of motion so obtained is exact within the context of general relativity for arbitrary media. The linear approximation is derived, and the double quasar 0957 + 561 is discussed. Publication: The Astrophysical Journal Pub Date: January 1983 DOI: 10.1086/160634 Bibcode: 1983ApJ...264..627N Keywords: Gravitational Effects; Photons; Quasars; Radiative Transfer; Refracted Waves; Relativity; Electromagnetic Fields; Equations Of Motion; Maxwell Equation; Particle Motion; Astrophysics full text sources ADS |

Absorption Spectrum of DNA for Wavelengths Greater than 300 nm

Although DNA absorption at wavelengths greater than 300 nm is much weaker than that at shorter wavelengths, this absorption seems to be responsible for much of the biological damage caused by solar radiation of wavelengths less than 320 nm. Accurate measurement of the absorption spectrum of DNA above 300 nm is complicated by turbidity characteristic of concentrated solutions of DNA. We have measured the absorption spectra of DNA from calf thymus, Clostridium perfringens, Escherichia coli, Micrococcus luteus, salmon testis, and human placenta using procedures which separate optical density due to true absorption from that due to turbidity. Above 300 nm, the relative absorption of DNA increases as a function of guanine-cytosine content, presumably because the absorption of guanine is much greater than the absorption of adenine at these wavelengths. This result suggests that the photophysical processes which follow absorption of a long-wavelength photon may, on the average, differ from those induced by shorter-wavelength photons. It may also explain the lower quantum yield for the killing of cells by wavelengths above 300 nm compared to that by shorter wavelengths.

Photochemical survival principle in molecular evolution

The role of solar radiation in molecular evolution is considered. The evolutionary trend is toward utilization of longer wavelength photons. In this process the short wavelength (ultraviolet) photons become detrimental and a protective atmosphere is becoming a necessity. It is proposed that for evolution to proceed, a conservation relation must be satisfied between the constructive and destructive actions of solar radiation on the one hand and the relative rates of biological synthesis and destruction on the other hand. This conservation relation requires that the rate of photosynthesis by visible light exceeds the photodestruction by the short ultraviolet. The thickness and absorbing properties of a selective atmosphere and the ratio of the quantum yield of synthesis to that of destruction are the parameters entering the conservation relation. Calculations have been performed of the minimum atmosphere necessary for later periods of molecular evolution.