Total Absorption Cross Section Research Articles

MMT Survey for Intervening MgiiAbsorption

We present the results from a spectroscopic survey for intervening Mg II absorption in the spectra of 381 background QSOs conducted at the MMT telescope. This survey complements our earlier SDSS EDR Mg II survey, extending our results to lower redshift (z 0.15) and weaker Mg II λ2796 rest equivalent width (W 0.1 A). We confirm two major results from that survey: the transition in the W distribution at W ≈ 0.3 A, and the W-dependent evolution of the incidence of systems. The nature of ∂2N/∂z∂W is consistent with the idea that multiple physically distinct components/processes contribute to the incidence of Mg II absorption systems in a W0-dependent manner and evolve at different rates. A significant decrease in the total proper absorption cross section is detected in our MMT data for systems as weak as 1.0 A ≤ W < 1.5 A at z 0.4. We discuss this W0-dependent evolution in the context of the evolution of galaxy structures, processes including superwinds and interactions, and damped-Lyα absorbers. We also consider the possibility that the observed redshift and W dependence of the incidence of absorption in spectroscopic surveys for low-ionization/neutral gas results from the effects of dust-induced extinction.

Bulk versus brane in the absorption and emission: 5d rotating black hole case

The absorption and emission spectra for the minimally-coupled brane and bulk scalar fields are numerically computed when the spacetime is a 5d rotating black hole carrying the two different angular momentum parameters a and b. The effect of the superradiant scattering in the spectra is carefully examined. It is shown that the low-energy limit of the total absorption cross section always equal to the area of the non-spherically symmetric horizon, i.e., 4 π ( r H 2 + a 2 ) for the brane scalar and 2 π 2 ( r H 2 + a 2 ) ( r H 2 + b 2 ) / r H for the bulk scalar where r H is an horizon radius. The energy amplification for the bulk scalar is roughly order of 10 −9% while that for the brane scalar is order of unity. This indicates that the effect of the superradiance is negligible for the case of the bulk scalar. Thus the standard claim that black holes radiate mainly on the brane is not changed although the effect of the superradiance is taken into account. The physical implication of this fact is discussed in the context of TeV-scale gravity.

Theory of the photodissociation of ozone in the Hartley continuum: Potential energy surfaces, conical intersections, and photodissociation dynamics

Ab initio potential energy and transition dipole moment surfaces are presented for the five lowest singlet even symmetry electronic states of ozone. The surfaces are calculated using the complete active space self consistent field method followed by contracted multireference configuration interaction (MRCI) calculations. A slightly reduced augmented correlation consistent valence triple-zeta orbital basis set is used. The ground and excited state energies of the molecule have been computed at 9282 separate nuclear geometries. Cuts through the potential energy surfaces, which pass through the geometry of the minimum of the ground electronic state, show several closely avoided crossings. Close examination, and higher level calculations, very strongly suggests that some of these seemingly avoided crossings are in fact associated with non-symmetry related conical intersections. Diabatic potential energy and transition dipole moment surfaces are created from the computed ab initio adiabatic MRCI energies and transition dipole moments. The transition dipole moment connecting the ground electronic state to the diabatic B state surface is by far the strongest. Vibrational-rotational wavefunctions and energies are computed using the ground electronic state. The energy level separations compare well with experimentally determined values. The ground vibrational state wavefunction is then used, together with the diabatic B<--X transition dipole moment surface, to form an initial wavepacket. The analysis of the time-dependent quantum dynamics of this wavepacket provides the total and partial photodissociation cross sections for the system. Both the total absorption cross section and the predicted product quantum state distributions compare well with experimental observations. A discussion is also given as to how the observed alternation in product diatom rotational state populations might be explained.

Experimental check of the GDH sum rule at MAMI and ELSA

An extensive experimental program was carried out at MAMI (Mainz) and ELSA (Bonn) to measure pion photo-production reactions on the nucleon in double polarization and to investigate the Gerasimov-Drell-Hearn Sum Rule. We obtained results for the proton in the energy range from about 200 MeV to 3000 MeV and for the neutron, using a deuteron target, from about 200 MeV to 1900 MeV. Preliminary results on the total absorption cross sections are presented and discussed.

Total cross sections for electron scattering at 10–5000 eV by polyatomic molecules CF 4, CF 3 H, C 2 F 4 , C 2 F 6 and C 2 H 3 F 3

The additivity rule and complex optical potential approach have been employed to obtain the total (elastic and absorption) cross sections for electron scattering by molecules (CF4, CF3H, C2F4, C2F6 and C2H3F3) over an incident energy range from 10 to 5000 eV. Compared with other calculations and experimental data wherever available, excellent agreement has been obtained. Above 1000eV, there are no experimental data for CF3H, C2F4, C2F6 and C2H3F3, so the present results can provide comparison and predictions for experimental research.

Absorption and emission spectra of an higher-dimensional Reissner–Nordström black hole

The absorption and emission problems of the brane-localized and bulk scalars are examined when the spacetime is a ( 4 + n ) -dimensional Reissner–Nordström black hole. Making use of an appropriate analytic continuation, we compute the absorption and emission spectra in the full range of particle's energy. For the case of the brane-localized scalar the presence of the nonzero inner horizon parameter r − generally enhances the absorptivity and suppresses the emission rate compared to the case of the Schwarzschild phase. The low-energy absorption cross section exactly equals to 4 π r + 2 , two-dimensional horizon area. The effect of the extra dimensions generally suppresses the absorptivity and enhances the emission rate, which results in the disappearance of the oscillatory pattern in the total absorption cross section when n is large. For the case of the bulk scalar the effect of r − on the spectra is similar to that in the case of the brane-localized scalar. The low-energy absorption cross section equals to the area of the horizon hypersurface. In the presence of the extra dimensions the total absorption cross section tends to be inclined with a positive slope. It turns out that the ratio of the missing energy over the visible one decreases with increase of r − .

Cross-sections for electron–imidogen radical (NH) collisions

In this work, we report a theoretical study on electron collisions with NH radicals in the low and intermediate energy ranges. Calculated elastic differential, integral and momentum-transfer cross-sections as well as grand-total (elastic+inelastic) and total absorption cross-sections for electron–NH collisions are reported in the (1–500)-eV range. A complex optical potential composed by static, exchange, correlation–polarization plus absorption contributions, derived from a fully molecular wave function, is used to describe the interaction dynamics. The Schwinger variational iterative method combined with the distorted-wave approximation is applied to calculate scattering amplitudes. Present calculated results are compared with the existing data for electron–NH scattering in the literature. Also, comparison made between our calculated cross-sections for elastic scattering with the theoretical and experimental results for electron–NH 3 collisions has revealed remarkable similarity even at incident energies as low as 1 eV.

Ab initio potential energy surfaces, total absorption cross sections, and product quantum state distributions for the low-lying electronic states of N2O

Adiabatic potential energy surfaces for the six lowest singlet electronic states of N(2)O (X (1)A('), 2 (1)A('), 3 (1)A('), 1 (1)A("), 2 (1)A(") and 3 (1)A(")) have been computed using an ab initio multireference configuration interaction (MRCI) method and a large orbital basis set (aug-cc-pVQZ). The potential energy surfaces display several symmetry related and some nonsymmetry related conical intersections. Total photodissociation cross sections and product rotational state distributions have been calculated for the first ultraviolet absorption band of the system using the adiabatic ab initio potential energy and transition dipole moment surfaces corresponding to the lowest three excited electronic states. In the Franck-Condon region the potential energy curves corresponding to these three states lie very close in energy and they all contribute to the absorption cross section in the first ultraviolet band. The total angular momentum is treated correctly in both the initial and final states. The total photodissociation spectra and product rotational distributions are determined for N(2)O initially in its ground vibrational state (0,0,0) and in the vibrationally excited (0,1,0) (bending) state. The resulting total absorption spectra are in good quantitative agreement with the experimental results over the region of the first ultraviolet absorption band, from 150 to 220 nm. All of the lowest three electronically excited states [(1)Sigma(-)(1 (1)A(")), (1)Delta(2 (1)A(')), and (1)Delta(2 (1)A("))] have zero transition dipole moments from the ground state [(1)Sigma(+)(1 (1)A('))] in its equilibrium linear configuration. The absorption becomes possible only through the bending motion of the molecule. The (1)Delta(2 (1)A('))<--X (1)Sigma(+)((1)A(')) absorption dominates the absorption cross section with absorption to the other two electronic states contributing to the shape and diffuse structure of the band. It is suggested that absorption to the bound (1)Delta(2 (1)A(")) state makes an important contribution to the experimentally observed diffuse structure in the first ultraviolet absorption band. The predicted product rotational quantum state distribution at 203 nm agrees well with experimental observations.

Elastic and absorption cross sections for electron–carbon monosulfide collisions

AbstractWe report a theoretical study of electron collisions on carbon monosulfide molecules in the low and intermediate energy range. Calculated differential, integral, and momentum–transfer cross sections for elastic e−–CS scattering as well as the total absorption cross sections are reported in the 1–500‐eV range. A complex optical potential composed by static, exchange, correlation–polarization, plus absorption contributions, derived from a fully molecular wave function, is used to describe the electron–molecule interaction dynamics. The Schwinger variational iterative method combined with the distorted‐wave approximation is applied to calculate the scattering amplitudes. Our calculated data are compared with the calculated and experimental results for electron scattering by an isoelectronic molecule N2O. Remarkable similarity in the cross sections is seen for these targets at incident energies of &gt;50 eV. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Theory of the photodissociation of ozone in the Hartley continuum; effect of vibrational excitation and O(1D) atom velocity distribution

The effect of vibrational excitation on the photodissociation cross section of ozone in the Hartley continuum is examined. The calculations make use of newly computed potential energy and transition dipole moment surfaces. The initial vibrational states of the ozone are computed using grid based techniques and the first few ab initio computed vibrational energy level spacings agree to within 10 cm(-1) with experimental values. The computed total absorption cross sections arising from different initial vibrational states of ozone are discussed in the light of the nature of the transition dipole moment surface. The computed cross section for excitation from the ground vibrational-rotational state is in good agreement with the experimentally measured cross section. Excitation of the asymmetric stretching vibration of ozone has a marked effect on both the form and magnitude of the photodissociation cross section. The velocity distributions of highly reactive O(1D) atoms arising from the photodissociation process in different wavelength ranges is also presented. The results show that the O(1D) atoms travel with a most probable translational velocity of 2.030 km s(-1) corresponding to a translational energy of 0.342 eV or 33.0 kJ mol(-1).

Elastic and absorption cross sections for electron–hydroxyl radical collisions

In this work, we report a theoretical study on electron collisions with $\mathrm{OH}$ radicals in the low and intermediate energy ranges. Calculated elastic differential, integral, and momentum-transfer cross sections as well as grand-total (elastic $+$ inelastic) and total absorption cross sections for electron-$\mathrm{OH}$ collisions are reported in the $1--500\text{\ensuremath{-}}\mathrm{eV}$ range. A complex optical potential composed by static, exchange, correlation-polarization plus absorption contributions, derived from a fully molecular wave function, is used to describe the interaction dynamics. The Schwinger variational iterative method combined with the distorted-wave approximation is applied to calculate scattering amplitudes. Present calculated results are compared with the existing data for electron-$\mathrm{OH}$ scattering in the literature. Also, comparison made between our calculated cross sections for elastic scattering with the theoretical and experimental results for electron-${\mathrm{H}}_{2}\mathrm{O}$ collisions has revealed remarkable similarity even at incident energies as low as $2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$.

Excited state electronic structures and dynamics of NOCl: a new potential function set, absorption spectrum, and photodissociation mechanism.

A set of analytical potential energy surfaces (PESs) for six singlet excited states of NOCl are constructed based on multireference configuration interaction calculations. The total absorption cross section at the energy range of 2-7 eV is calculated by quantum dynamics calculations with the present PESs and transition dipole moments. The calculated absorption spectrum agrees well with the experiment. It is also found that the A band with the absorption maximum at 6.3 eV is attributed to the transition to the 4 1A' state, though the excitations to the 3 1A' and 3 1A" states contribute to the spectrum at the energy range between 4 and 5 eV. The spin-forbidden transitions are concluded to be negligibly weak. The mechanism of photodissociation reaction at the energy region corresponding to the A band is examined. The nonadiabatic transition rates from the 4 1A' state to lower singlet and triplet states are estimated by Fermi's golden rule, and the transitions to the 1 1A' and 3 1A' states induced by vibronic coupling are found to be the predominant dissociation pathways. The experimentally observed energy dependence of the recoil anisotropy of the fragments is discussed based on the calculated nonadiabatic transition rates.

Nuclear photoabsorption at photon energies between 300 and 850 MeV

We construct the formula for the photonuclear total absorption cross section using the projection method and the unitarity relation. Our treatment is very effective when interference effects in the absorption processes on a nucleon are strong. The disappearance of the peak around the position of the $D_{13}$ resonance in the nuclear photoabsorption can be explained with the cooperative effect of the interference in two-pion production processes,the Fermi motion, the collision broadenings of $\Delta$ and $N^*$, and the pion distortion in the nuclear medium. The change of the interference effect by the medium plays an important role.

Electronic and vibrational predissociation in ArI2 photodissociation dynamics

Quantum dynamical calculations on the photodissociation process: ArI2(X)+hν→Ar+I2(B) or Ar+I+I have been performed using diatomics-in-molecule semiempirical potential energy surfaces in the spectral region of the I2(B,v=15–25)←I2(X,v=0) transition. The B state responsible for vibrational predissociation producing Ar+I2(B) is coupled to four dissociative states inducing electronic predissociation to Ar+I(2P3/2)+I(2P3/2). These dissociative states correlate to the a(1g), a′(0g+), B″(1u), 1(2g) electronic states of I2. Both linear and perpendicular initial ArI2(X) isomers are considered. For the linear isomer, only the a′ state has non-negligible effect on photodissociation dynamics, although total photon absorption cross sections are not significantly modified when coupling to a′ is taken into account, partial cross sections corresponding to vibrational predissociation are smaller. For the perpendicular isomer, resonance decay rates are increased, mainly by the coupling to a′(0g+), 1(2g), and a(1g) states. Decay rates oscillate as a function of the vibrational excitation of I2(B) but the main source of oscillation is the intramolecular vibrational energy redistribution which occurs in vibrational predissociation, rather than Franck–Condon oscillations in electronic predissociation.

Causality violation and naked time machines in AdS5

We study supersymmetric charged rotating black holes in AdS$_5$, and show that closed timelike curves occur outside the event horizon. Also upon lifting to rotating D3 brane solutions of type IIB supergravity in ten dimensions, closed timelike curves are still present. We believe that these causal anomalies correspond to loss of unitarity in the dual ${\cal N}=4$, D=4 super Yang-Mills theory, i.e. the chronology protection conjecture in the AdS bulk is related to unitarity bounds in the boundary CFT. We show that no charged or uncharged geodesic can penetrate the horizon, so that the exterior region is geodesically complete. These results still hold true in the quantum case, i.~e.~the total absorption cross section for Klein-Gordon scalars propagating in the black hole background is zero. This suggests that the effective temperature is zero instead of assuming the naively found imaginary value.

Dissociative photoionization of CF4 from 23 to 120 eV

Using synchrotron radiation as a continuum light source, dissociative photoionization of CF4 has been studied in the photon-energy region of 23–120 eV. Ion branching ratios were obtained by analyzing time-of-flight mass spectra and were converted to the absolute partial cross sections for the production of singly charged CF3+, CF2+, CF+, F+, and C+ ions, as well as doubly charged CF32+ and CF22+ ions by using the reported total absorption cross sections of CF4. Ion branching ratios were differentiated with respect to the incident photon energy. The results obtained by this analytical photoion spectroscopy clearly show dissociation pathways of the CF4+ and CF42+ ions, many of which are observed for the first time in the present study. These pathways are discussed by comparing with the reported electronic states of the ions.

Photodisintegration of three-body nuclei with realistic 2N and 3N forces

Total photonuclear absorption cross sections of 3 H and 3 He are studied using realistic NN and NNN forces. Final state interactions are fully included. Two NN potential models, the AV14 and the r-space Bonn-A potentials, are considered. For the NNN forces the Urbana-VIII and Tucson-Melbourne models are employed. We find the cross section to be sensitive to nuclear dynamics. Of particular interest in this work is the effect which NNN forces have on the cross section. The addition of NNN forces not only lowers the peak height but increases the cross section beyond 70 MeV by roughly 15%. Cross sections are computed using the Lorentz integral transform method.

Multiproton final states in positive pion absorption below theΔ(1232)resonance

Inclusive cross sections for positive pion absorption leading to final states including two or more protons have been measured with a large solid angle detector for incident pion energies from 30 to 135 MeV for targets with $A=2--208.$ The mass dependences for the inclusive $({\ensuremath{\pi}}^{+},2p),$ $({\ensuremath{\pi}}^{+},3p),$ and total absorption cross sections for multiproton final states were found to be proportional to ${A}^{n}$ with $n\ensuremath{\approx}0.5.$ These cross sections also were observed to have an energy dependence at energies below 150 MeV reflective of the importance of the $\ensuremath{\Delta}(1232)$ resonance, similar to that observed for $\ensuremath{\pi}\stackrel{\ensuremath{\rightarrow}}{d}\mathrm{pp}.$ The inclusive cross sections for $({\ensuremath{\pi}}^{+},4p)$ were found to be less than 10 mb for all targets at all energies. Estimates were also obtained for cross sections for pion absorption leading to $2p1n$ and $3p1n$ final states. Quasideuteron absorption contributions increase slowly with A, and the energy dependence of those contributions mirrors that for $\ensuremath{\pi}\stackrel{\ensuremath{\rightarrow}}{d}\mathrm{pp}.$ The data obtained here for multiproton final states indicate that a significant fraction of absorption events, increasing with A, most likely arises from final states containing fewer than two protons.

Resonant two-photon absorption in ZnSiP2

The complex of optical investigations into the intrinsic (I) and resonant (R) two-photon absorption (TPA) inZnSiP2 crystals of tetragonal modifications is performed by methods of amplitude laser-modulation spectroscopy. The ITPA of allowed-forbidden type and the two Lorentz spectral lines associated with coherent resonant two-photon transitions through impurity states of allowed-allowed type are found. The electron transverse relaxation time at the RTPA is determined, and the total absorption cross section of laser-radiation photons emitted at electron transitions between the valence band v, the conduction band c, and local centers that produce real states intermediate for the RTPA in the forbidden band is estimated.

π+absorption on N and Ar

The absorption of positive pions on N and Ar has been studied for Tπ+=118, 162, and 239 MeV. A precise determination has been made of the total absorption cross section for each energy and target nucleus. Comparisons are made with prior LADS results on 2H, 3He, and 4He. In addition, results are presented for the detected multiplicities of emitted protons, neutrons, and deuterons following pion absorption.Received 14 May 1999DOI:https://doi.org/10.1103/PhysRevC.60.054610©1999 American Physical Society