Absolute Total Cross Sections Research Articles

Measurement ofνμ-induced charged-current neutral pion production cross sections on mineral oil atEν∈0.5–2.0 GeV

Using a custom 3 \v{C}erenkov-ring fitter, we report cross sections for $\nu_\mu$-induced charged-current single $\pi^0$ production on mineral oil (\chtwo) from a sample of 5810 candidate events with 57% signal purity over an energy range of $0.5-2.0$GeV. This includes measurements of the absolute total cross section as a function of neutrino energy, and flux-averaged differential cross sections measured in terms of $Q^2$, $\mu^-$ kinematics, and $\pi^0$ kinematics. The sample yields a flux-averaged total cross section of $(9.2\pm0.3_{stat.}\pm1.5_{syst.})\times10^{-39}$cm$^2$/CH$_2$ at mean neutrino energy of 0.965GeV.

Total electron-scattering cross section measurements for tetrahydropyran, (CH2)5O, molecules

Absolute total cross section (TCS) for electron scattering from tetrahydropyran (THP: (CH2)5O) molecules has been measured from 1 to 400 eV, using a linear electron transmission technique. The TCS energy function for electron–THP collisions is characterized by the broad enhancement spanned between 3 and 15 eV, which can be attributed to resonant processes. Comparison is also made between the present results for THP and earlier TCS measurements for tetrahydrofuran (THF: (CH2)4O) and α-tetrahydrofurfuryl alcohol (THFA: C5H10O2).

Threshold photoelectron source for the study of low-energy electron scattering: Total cross section for electron scattering from krypton in the energy range from 14 meV to 20 eV

An experimental technique for the measurement of the total cross section for electron scattering from atoms and molecules at high resolution is described. The total cross sections for electron scattering from Kr in the energy range from 14 meV to 20 eV obtained with the technique are also reported. The present technique employs a combination of the penetrating field technique and the threshold photoionization of rare-gas atoms using synchrotron radiation as an electron source in order to produce a high-resolution electron beam at very low energy. The characteristics of the electron sources were determined by measuring the ionizing photon energy dependence of photoelectron yield. Absolute total cross sections for electron scattering are obtained by the attenuation method. The measured absolute values of the total cross sections for electron scattering from Kr agree with those obtained by other groups down to 175 meV, above which several experimental works have been reported. Below 175 meV, the present results generally agree with theoretical cross sections down to 14 meV. The resonant structures in the total cross sections due to Kr${}^{\ensuremath{-}}$ ($4{p}^{5}5{s}^{2 2}{P}_{3/2}$) and the Kr${}^{\ensuremath{-}}$ ($4{p}^{5}5{s}^{2 2}{P}_{1/2}$) Feshbach resonances are also reported. The resolution of the present setup has been estimated from a fit of the measured profile of the Kr${}^{\ensuremath{-}}$ ($4{p}^{5}5{s}^{2 2}{P}_{3/2}$) resonance by the theoretical curve obtained from the resonant scattering theory.

Absolute differential and total cross sections for neutral fragments from dissociative collisions of triatomic hydrogen like ions on He

Neutral fragment products from dissociative collisions of triatomic hydrogen like ions incident on He atoms were studied. Absolute differential and total cross sections are reported here in the energy range of 1.00–5.00 keV and scattering angles between −5.0° and 5.0°. The differential cross sections show decreasing behaviour with a slight structure around 2.0°. The total cross sections for all triatomic molecular ions studied in this work are found to be comparable for the same velocity (E/M). The measured cross sections are between 0.7 × 10−17 cm2 and 0.9 × 10−16 cm2. The present results for the neutral total cross section correlate very well with previously measured total ions cross section for H+3, D+3 and HD+2 on He.

Cross sections for electron scattering from furan molecules: Measurements and calculations

Electron-scattering cross sections have been determined for the furan (C${}_{4}$H${}_{4}$O) molecule, both experimentally and theoretically. An absolute total cross section (TCS) has been measured over energies from 0.6 to 400 eV using a linear electron-transmission method. The TCS energy function is dominated with a very broad enhancement, between 1.2 and 9 eV; on the low-energy side, some resonant structures are visible. Integral elastic (ECS) and ionization (ICS) cross sections have been also calculated up to 4 keV in the additivity rule approximation and the binary-encounter-Bethe approach, respectively. Their sum, ECS$+$ICS, is in a very good agreement with the measured TCS above 70 eV.

Electron-capture cross sections forLi+colliding on H andH2in the low-keV energy region

Absolute total and differential cross sections have been measured for neutral Li formation in single collisions of Li{sup +} on H{sub 2} from 1 to 5 keV. Total cross sections were obtained by direct integration of measured differential cross sections and are in good agreement with earlier cross-sectional measurements. A comparison of the differential cross sections plotted as a function of the reduced variables {theta}sin{theta}d{sigma}/d{Omega} vs E{theta} is also presented with a comparison of the maximum of the curves of the present data. Theoretically, we report state to state and summed charge transfer at collision energies ranging from 0.1 to 25 keV/amu. Cross sections were calculated using a nonadiabatic time-dependent direct approach for study of ion-atom and ion-molecule interaction processes. We verify that the main electron-capture channel is in the n=2 state of Li with a large probability for electron capture for impact parameters below 2 a.u. for collisions on both H and H{sub 2} in the so-called rotational region of the collision. In the case of atomic hydrogen, the electron-capture probability into the 2s and 2p states shows an oscillating behavior that smooths out when summed. For the molecular case, we find that for projectile energies larger than 1more » keV, ionization effects become important. Our results show good agreement when compared to other available experimental and theoretical data.« less

Absolute total and partial cross sections for ionization of nucleobases by proton impact in the Bragg peak velocity range

We present experimental results for proton ionization of nucleobases (adenine, cytosine, thymine, and uracil) based on an event-by-event analysis of the different ions produced combined with an absolute target density determination. We are able to disentangle in detail the various proton ionization channels from mass-analyzed product ion signals in coincidence with the charge-analyzed projectile. In addition we are able to determine a complete set of cross sections for the ionization of these molecular targets by 20--150 keV protons including the total and partial cross sections and the direct-ionization and electron-capture cross sections.

II. Electron-impact dissociative excitation of C2H 2 + and C2D 2 +

Absolute cross-sections for electron-impact dissociative excitation of C2H (2) (+) and C2D (2) (+) to C2D+, CH+, C+, C (2) (+) , H+ and CH (2) (+) singly-charged fragments have been estimated. The animated crossed-beams method is applied in the energy range from the corresponding reaction threshold up to 2.5 keV. Individual contributions for dissociative excitation are determined from the analysis of the total absolute cross-sections measured for each detected product. The dissociative excitation cross-sections are seen to decrease for more than an order of magnitude, from C2D+ (12.6 +/- 0.3) x 10(-17) cm(2) over CH+ (6.37 +/- 0.12) x 10(-17) cm(2), C+ (4.09 +/- 0.13) x 10(-17) cm(2), C (2) (+) (3.5 +/- 0.2) x 10(-17) cm(2) and H+ (1.57 +/- 0.11) x 10(-17) cm(2) to CH (2) (+) (3.6 +/- 0.5) x 10(-18) cm(2). Cross-section values and threshold energies are compared with the data which are available from the literature.

Dissociative electron attachment in nonplanar chlorocarbons with π∗/σ∗-coupled molecular orbitals

Total absolute cross sections for the dissociative electron attachment (DEA) process are reported for a series of nonplanar ethylenic and phenylic compounds monosubstituted with (CH(2))(n)Cl groups, where n=1-4. Coupling between the local pi* molecular orbitals provided by the unsaturated moieties and the sigma* (C-Cl) orbital is thus examined as a function of the separation of these groups. In particular, the coupling is viewed from the perspective of the interacting temporary negative ions formed by short lived occupation of these orbitals and their decay into the DEA channel. A theoretical treatment of "remote" bond breaking, presented elsewhere, satisfactorily accounts for DEA in the chloroethylenic compounds presented here and emphasizes not only the delocalization of the coupled anionic wave functions but the importance of their relative phases. The dependence of the cross sections on the vertical attachment energies, measured by electron transmission spectroscopy, is also explored and compared to that found previously in chlorinated alkanes.

Scattering of electrons from acetaldehyde and acetone

Absolute total cross sections (TCSs) for electron scattering from acetaldehyde [(CH3)CHO] and acetone [(CH3)2CO] molecules have been measured at electron-impact energy extending from 0.7 to 400 eV, using a linear electron-transmission technique. The shape of obtained TCS energy dependences appears typical for targets of high electric dipole moment; both TCSs decrease with the energy increase; only between 4 and 12 eV is a weak enhancement in TCSs is clearly perceptible. The experimental TCSs for (CH3)CHO and for (CH3)2CO are also compared with those for their cyclic isomeric counterparts: c-(CH2)2O and c-(CH2)3O, respectively.

Experimental investigation of atomic collisions in time scales varying from nanosecond to microseconds

We present the results from two experiments investigating collisions that differ in time scale by three orders of magnitude. The first experiment enables the determination of absolute total collision cross sections using a technique that measures a change in the loss rate of trapped atoms from a magneto optical trap (MOT). We also investigate light assisted collision processes between cold metastable neon atoms in the 3P2 metastable state within the MOT. A catalysis laser is scanned in frequency across the 3P2 – 3D3 cooling transition and the ionization rate was observed. Ionization spectra are obtained which demonstrate a dependence on the magnetic sublevels of the transition that the catalysis laser is exciting.

Total electron scattering cross sections for methanol and ethanol at intermediate energies

Absolute total cross section (TCS) measurements of electron scattering from gaseous methanol and ethanol molecules are reported for impact energies from 60 to 500 eV, using the linear transmission method. The attenuation of intensity of a collimated electron beam through the target volume is used to determine the absolute TCS for a given impact energy, using the Beer–Lambert law to first approximation. Besides these experimental measurements, we have also determined TCS using the additivity rule.

Total cross sections for electron capture processes in slow collisions of Ne6+ ions with H2O and CO2

Using the translation energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture by Ne6+ ions from H2O and CO2 at laboratory impact energies between 250 and 3000 eV.

Absolute Total np and pp Cross-Section Determinations

Absolute total cross sections for np and pp scattering below 1000 MeV are determined based on partial-wave analyses (PWAs) of nucleon-nucleon scattering data. These cross sections are compared with most recent ENDF/B and JENDL data files, and the Nijmegen PWA. Systematic deviations from the ENDF/B and JENDL evaluations are found to exist in the low-energy region.

High-resolution electron attachment to the molecules CCl4 and SF6 over extended energy ranges with the (EX)LPA method

Using a variant of the laser photoelectron attachment (LPA) method with an extended energy range (EXLPA), we have studied low-energy electron attachment to the molecules CCl4 (Cl− and Cl−2 formation) and SF6 (SF−6 and SF−5 formation) in a diffuse gas target (TG = 300 K) from 0 eV up to 2 eV at energy widths down to 14 meV. In the EXLPA method, pulses of near-zero energy photoelectrons are produced in a guiding magnetic field, accelerated by a weak electric field, brought to the energy of interest prior to their traversal through the target region and subsequently accelerated and deflected onto a detecting plate. Anions due to electron attachment are extracted by a pulsed electric field, during which the photoelectron current is interrupted, and detected by a quadrupole mass spectrometer. The EXLPA anion yields are combined with absolute cross sections, obtained at very high resolution (≈1 meV) with the LPA method over the range 0–0.17 eV, to yield new recommended absolute partial and total attachment cross sections over the range 0–2 eV at the well-defined gas temperature TG = 300 K. Our cross sections show characteristic deviations from previously reported results. At least in part, these differences can be attributed to the fact that in the earlier electron beam experiments the gas temperature was higher than 300 K. For SF6, the branching fractions for SF−5 formation at electron energies 0.002–0.43 eV and for different initial rovibrational distributions are compared with those recently predicted from kinetic modelling within the framework of statistical unimolecular rate theory. Satisfactory agreement is observed, but our data provide evidence that an additional path for producing SF−6 and SF−5 ions is available at electron energies above about 0.3 eV.

Electron scattering by trimethylene oxide, c-(CH2)3O, molecules

Electron-scattering cross sections have been determined for trimethylene oxide, cyclic (CH(2))(3)O molecule, both experimentally and theoretically. The absolute total cross section (TCS) has been measured over energies from 1 to 400 eV using a linear electron-transmission method. The obtained TCS generally decreases with rising energy, except for the 3-10 eV range, where some resonantlike structures are discernible. Integral elastic cross section (ECS) and ionization cross section (ICS) have been also calculated up to 3 keV in the additivity rule approximation and the binary-encounter-Bethe approach, respectively. Their sum, ECS+ICS, is in a good agreement with the measured TCS. Comparison of the TCS energy dependence for trimethylene oxide with that for its isomeric open-chain counterpart--acetone, (CH(3))(2)CO, has also been made. Moreover, examination of experimental TCSs for the cyclic (CH(2))(n)O, n=2-4, ether series reveals that the intermediate-energy molecular TCSs for members of that family can be nicely represented as a sum of the effective TCSs for particular constituents of the molecule, i.e., methylene groups and oxygen atom. Finally, based on these partial TCSs, the TCS for the c-(CH(2))(5)O--the next member of the series--has been determined and compared with the respective ECS+ICS values computed here for this compound.

Absolute photodetachment cross section measurements of the O− and OH− anion

Absolute total photodetachment cross sections of O(-) and OH(-) anions stored in a multipole radio frequency trap have been measured using a novel laser depletion tomography method. For OH(-) the total cross sections of 8.5(1)(stat)(3)(syst) and 8.1(1)(stat)(7)(syst)x10(-18) cm(2), measured at 662 and 632 nm, respectively, were found constant in the temperature range of 8-300 K. The O(-) cross sections 5.9(1)(stat)(2)(syst) and 6.3(1)(stat)(2)(syst)x10(-18) cm(2) measured at 170 K at 662 and 532 nm, respectively, agree within error estimations with preceding experiments and increase the accuracy of the widely used calibration standard for relative photodetachment measurements of diverse atomic and molecular species.

Double capture cross sections inp−Arcollisions

$p\text{\ensuremath{-}}\mathrm{Ar}$ collisions are investigated theoretically and experimentally at impact energies in the keV regime. Total cross sections for double electron capture of $p$ on Ar are calculated by an independent-particle method in the impact energy range $3--100\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. We have measured the absolute differential and total cross sections for double electron capture for $1.0--5.0\text{\ensuremath{-}}\mathrm{keV}$ $p\text{\ensuremath{-}}\mathrm{Ar}$ collisions. The absolute differential cross section (DCS) for all the collision energies considered shows a decreasing behavior with increasing angle, exhibiting an overall decrease of three orders of magnitude. The integrated DCS is found to be between the range of $0.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ and $4.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{2}$, displays an increasing behavior as a function of the incident energy, and merges with previous data at the high-energy side. The theoretical total cross sections reproduce the structures around $5\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ and $15\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ reported by other available measurements. The analysis of the capture into the $1{s}^{1}4{s}^{1}$ hydrogen-like configuration points in the direction of a common origin for these peaks.

Absolute partial cross sections and kinetic energy analysis for the electron impact ionization of ethylene

We present absolute partial electron impact ionization cross sections for ethylene in the electron energy range between threshold and 1000 eV measured with a two sector field double focusing mass spectrometer. Ion kinetic energy distribution functions have been measured at all electron energies by applying a deflection field method. Multiplication of the measured relative cross sections by the appropriately determined discrimination factors lead to accurate relative partial cross sections. Normalization of the sum of the relative partial cross sections to an absolute total cross section gives absolute partial cross section values. The initial kinetic energy distributions of several fragment ions show the presence of two or more contributions that exhibit different electron energy dependencies. Differential cross sections with respect to the initial kinetic energy of the ions are provided and are related to specific ion production channels. The electron threshold energies for the direct and numerous other dissociative ionization channels are determined by quantum chemical calculation and these allow the determination of the total kinetic energy release and the electron energy loss for the most prominent dissociative ionization channels.

Low-energy electron attachment to chloroform (CHCl3) molecules: A joint experimental and theoretical study

Results from a joint experimental and theoretical study of electron attachment to chloroform (CHCl3) molecules in the gas phase are reported. In an electron swarm study involving a pulsed Townsend technique with equal gas and electron temperatures, accurate attachment rate coefficients were determined over the temperature range 295–373K; they show an Arrhenius-type rise with increasing temperature, corresponding to an activation energy of 0.11(1)eV. In a high resolution electron beam experiment involving two versions of the laser photoelectron attachment method, the relative cross section for Cl− formation from CHCl3 over the energy range 0.001–1.25eV at the gas temperature TG=300K was measured. It exhibits clear downward cusp structure at the threshold for excitation of one quantum of the vibrational symmetric deformation mode ν3, indicating that this mode is active in the primary attachment process. With reference to our thermal attachment rate coefficient k(T=300K)=3.9(2)×10−9cm3s−1, a new highly resolved absolute attachment cross section for TG=300K was determined. This cross section is extended to higher energies by measurements, carried out with a pulsed electron beam apparatus which also provided new data for the distinctly weaker fragment anions HCl2− and CCl2−. The resulting total absolute cross section for anion formation is used to calculate the dependence of the attachment rate coefficient k(Te;TG) on electron temperature Te over the range 50–15000K at the fixed gas temperature TG=300K. In addition, we report the dependence of the relative cross section for Cl− formation on gas temperature (TG=310–435K). For comparison with the experimental data, R-matrix calculations have been carried out for the dominant anion channel Cl−. The results recover the main experimental observations and predict the dependence of the DEA cross section on the initial vibrational level ν3 and on the vibrational temperature. Our results are compared with those of previous electron beam and electron swarm experiments.