Search results for "absorption."
showing 10 items of 2682 documents
High-resolution spectrum of the ν+ν(E),ν+ν(E),ν+ν(A), and ν3+ν4(A2) bands of the PH3 molecule: assignments and preliminary analysis
2004
Abstract The high-resolution (0.005 cm −1 ) Fourier transform infrared spectrum of PH3 is recorded in the region between 3280 and 3580 cm −1 where the following bands are located: ν 1 +ν 4 (E), ν 3 +ν 4 (E), ν 3 +ν 4 (A 1 ) , forbidden on symmetry band ν3+ν4(A2), and very weak bands ν 1 +ν 2 (A 1 ), ν 2 +ν 3 (E) . Transitions are assigned to the first four ones. Vibrational analysis of known experimental data is made.
High-resolution spectroscopy and preliminary global analysis of C–H stretching vibrations of C2H4 in the 3000 and 6000cm−1 regions
2010
Abstract Ethylene (ethene, H2C=CH2) is a naturally occurring compound in ambient air that affects atmospheric chemistry and global climate. The C2H4 spectrum is available in databases only for the 1000 and 3000 cm−1 ranges. In this work, the ethylene absorption spectrum was measured in the 6030–6250 cm−1 range with the use of a high resolution Bruker IFS 125HR Fourier-spectrometer and a two-channel opto-acoustic spectrometer with a diode laser. As a secondary standard of wavelengths, the methane absorption spectrum was used in both cases. A preliminary analysis was realized thanks to the tensorial formalism developed by the Dijon group that is implemented in the XTDS software package [39] .…
Influence of the time-coherence of light on the absorption lineshapes of low-pressure gases
2001
Abstract A property of ultrashort laser pulses, their redshift by interaction with matter, is extended to ordinary time-incoherent light by a change of the scale of time. It appears that the matter must be a gas at a pressure uncommonly low in the labs, and that the gas must have a hyperfine structure. The relative frequency shift is constant as a Doppler shift; the images are not blurred because the interaction is space-coherent. In the presence of a redshift, the absorption lines cannot be seen because they are as wide as the shift. This interaction may produce a part of the cosmological redshift, the energy lost at high frequencies being transferred to the 2.7 K radiation. The interactio…
Modeling the energy thermalization of X-ray photons in a microcalorimeter with superconducting absorber
2003
We present a modeling of the response of a microcalorimeter to the absorption of X-ray photons, based on the main microscopical processes responsible for the energy thermalization. In particular, we have modeled a microcalorimeter with superconducting tin absorber (350 micron x 350 micron x 7 micron) and neutron transmutation doped (NTD) germanium thermistor (75 micron x 50 micron x 150 micron). Such a detector, operated at 60 mK, is expected to achieve a spectral resolution as good as 1 eV FWHM in the soft X-ray energy range, based on the known sources of thermal and electronic noise. Nevertheless, the best spectral resolution measured in laboratory experimental tests is of about 5 eV FWHM…
Branching fraction measurements of arsenic 4p25s-4p3 transitions
2021
Abstract Transition lines of neutral arsenic atom (As I) have been observed in the spectra of stellar and sub-stellar objects. Accurate and reliable data of oscillator strengths of those transitions allow differentiating between different evolution models of those objects. We have measured branching fractions for As I (4p25s-4p3) transition lines in 180–310 nm spectral range with higher increased accuracy using light source powered by inductively coupled radio frequency plasma (RF-ICP) source – not earlier applied in studies of atomic arsenic. The measurements were performed for 7 excited states of As I and compared with data from the literature. We combined them with the selected lifetime …
The Influence of Absorption on the Extinction of Solar and Sky Radiation
1965
The purpose of this paper is to investigate the influence of absorption of the aerosol particles on the extinction of solar and sky radiation. The efficiency factors have been computed as well as the extinction, the scattering, the absorption, and the scattering function for the whole turbid atmosphere with help of the Mie theory for a complex index of refraction for a more or less absorbent medium. From these values the intensities of diffuse sky radiation have been obtained. The extinction and absorption coefficients increase for a more absorbent atmosphere, whereas the scattering coefficient decreases. The imaginary part of the complex index of refraction effects an increasing attenuatio…
The complex enviroment around Cir X-1
2008
We present the results of an archival 54 ks long Chandra observation of the peculiar source Cir X–1 during the phase passage 0.223-0.261, based on the phase zero passage at the periastron, of its orbital period. We focus on the study of detected emission and absorption features using the High Energy Transmission Grating Spectrometer on board of the Chandra satellite. A comparative analysis of X-ray spectra, selected at different flux levels of the source, allows us to distinguish between a very hard state, at a low countrate, and a brighter, softer, highly absorbed spectrum during episodes of flaring activity, when the unabsorbed source luminosity is about three times the value in the hard …
Magnetohydrodynamic Modeling of the Accretion Shocks in Classical T Tauri Stars: The Role of Local Absorption in the X-Ray Emission
2014
We investigate the properties of X-ray emission from accretion shocks in classical T Tauri stars (CTTSs), generated where the infalling material impacts the stellar surface. Both observations and models of the accretion process reveal several aspects that are still unclear: the observed X-ray luminosity in accretion shocks is below the predicted value, and the density versus temperature structure of the shocked plasma, with increasing densities at higher temperature, deduced from the observations, is at odds with that proposed in the current picture of accretion shocks. To address these open issues we investigate whether a correct treatment of the local absorption by the surrounding medium …
Long term X-ray spectral variability of the nucleus of M81
2003
We have analysed the soft X-ray emission from the nuclear source of the nearby spiral galaxy M81, using the available data collected with ROSAT, ASCA, BeppoSAX and Chandra. The source flux is highly variable, showing (sometimes dramatic: a factor of 4 in 20 days) variability at different timescales, from 2 days to 4 years, and in particular a steady increase of the flux by a factor of >~ 2 over 4 years, broken by rapid flares. After accounting for the extended component resolved by Chandra, the nuclear soft X-ray spectrum (from ROSAT/PSPC, BeppoSAX/LECS and Chandra data) cannot be fitted well with a single absorbed power-law model. Acceptable fits are obtained adding an extra component, …
Linestrengths of the ν2 and ν4 bands of 12CH4 and 13CH4
1989
Absorption spectra recorded on the high-resolution Fourier transform spectrometer at Kitt Peak National Observatory/National Solar Observatory were used to measure individual line strengths of the nu(2) and nu(4) bands of (C-12)H4 and (C-13)H4. The measurements were used to obtain expressions that could be used to correctly predict individual line strengths through five orders of magnitude of absorption strength and high values of J-prime. Transition strengths were modeled using the dyad formalism of two interacting bands and a seven-term second-order dipole-moment expansion. The successful fitting of these data indicates that the method can be used to model measurements of 2- to 5-percent …