Energy Dependence Of Cross Section Research Articles

Nuclear reaction cross sections and the optical potentials and for the n-12C and N-12C scattering

In this talk we first discuss total cross sections for the system n-12C in the incident energy range 20-500 MeV, calculated with a phenomenological optical potential and the optical model. We compare with calculations done with the eikonal model using the same potential and a single folding potential in the optical limit. Several single folding potentials are obtained using 12C densities from different models. These potentials are sensitive to the density used and none of them reproduces the characteristics of the phenomenological potential nor the cross section results. We then discuss nucleus-nucleus potentials and reaction cross sections for some projectiles on 12C within the eikonal formalism. We find that single folded projectile-target imaginary potentials and double folded potentials can produce similar energy dependence of the reaction cross sections but the single folding results agree better with experimental data provided the radius parameter of the phenomenological n-target potential is allowed to be energy dependent. We conclude that a single folding nucleusnucleus potential build on a phenomenological nucleon-nucleus potential can constitute an interesting and useful alternative to double folding potentials.

Electron-induced ionization cross-sections for C5H5N

The secondary electron energy-dependent partial differential ionization cross sections at fixed incident electron energies 100 and 200 eV and their integral or total ionization cross sections in the incident electron energy range ionization threshold to 5 keV for C5H5N Bio-molecule due to electron impact corresponding to the produced major cations are calculated by employing revisited Jain-Khare semiempirical approach. The averaged secondary electron energy and the ionization rate coefficients are calculated from the ionization threshold to 5 keV. The present results are compared with available experimental and theoretical results and are found to be in satisfactory agreement.

Measurement of e+e−→pK−Λ¯+c.c.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {e}^{+}{e}^{-}\ o p{K}^{-}\\overline{\\Lambda}+c.c. $$\\end{document} cross sections between 4.009 GeV and 4.951 GeV

Using e+e− collision datasets corresponding to a total integrated luminosity of 21.7 fb−1 collected with the BESIII detector at the BEPCII collider at center-of-mass energies ranging from 4.009 GeV to 4.951 GeV, the energy-dependent cross sections of e+e−→pK−Λ¯+c.c.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {e}^{+}{e}^{-}\ o p{K}^{-}\\overline{\\Lambda}+c.c. $$\\end{document} are measured for the first time. By fitting these energy-dependent cross sections, we search for the excited ψ states ψ(4160) and ψ(4415), and the vector charmonium-like states ψ(4230), ψ(4360), and ψ(4660). No evidence for these is observed and the upper limits on the branching fractions of these states decaying into pK−Λ¯+c.c.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ p{K}^{-}\\overline{\\Lambda}+c.c. $$\\end{document} are set at the 90% confidence level.

Precise Measurement of the e^{+}e^{-}→D_{s}^{*+}D_{s}^{*-} Cross Sections at Center-of-Mass Energies from Threshold to 4.95GeV.

The process e^{+}e^{-}→D_{s}^{*+}D_{s}^{*-} is studied with a semi-inclusive method using data samples at center-of-mass energies from threshold to 4.95GeV collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections of the process are measured for the first time with high precision in this energy region. Two resonance structures are observed in the energy-dependent cross sections around 4.2 and 4.4GeV. By fitting the cross sections with a coherent sum of three Breit-Wigner amplitudes and one phase-space amplitude, the two significant structures are assigned masses of (4186.8±8.7±30) and (4414.6±3.4±6.1) MeV/c^{2}, widths of (55±15±53) and (122.5±7.5±8.1) MeV, where the first errors are statistical and the second ones are systematic. The inclusion of a third Breit-Wigner amplitude is necessary to describe a structure around 4.79GeV.

Coupled channels and production of near-threshold [formula omitted] resonances in e+e− annihilation

The effects of final-state interaction of hadrons, produced in e+e− annihilation near the threshold, are discussed. If there is a loosely bound state or a virtual state in a system of produced hadrons, then the energy dependence of hadroproduction cross section is very strong. Our approach is based on the use of the effective potentials accounting for the interaction between hadrons in the final state. The cases of a few channels with nonzero transition amplitudes between them are considered. It is shown that these transitions drastically change the energy dependence of the cross sections. In particular, a narrow resonance below the threshold in one channel leads to a broad peak in another channel. We explained the non-trivial energy dependence of the production cross sections of BB¯, B⁎B¯, BB¯⁎, B⁎B¯⁎ near the thresholds in e+e− annihilation and obtained good agreement between our predictions and the experimental data available.

Exclusive Photo-production of J/Ψ and Ψ(2s) as a tool to explore the transition to high and saturated gluon densities at the LHC.


 
 
 We study the energy dependence of the cross-section for exclusive photo-production of vector mesons J/Ψ and Ψ(2s) and search for signs for the onset of non-linear QCD dynamics in this observable. Our study is based on two dipole models: the Golec-Biernat, Wuesthoff Model (GBW) and the Bartels, Golec-Biernat, Kowal- ski Model (BGK). We find that differences between linear and non-linear implementations of these models are relatively small in the kinematic region probed by both HERA and LHC experiments if the energy dependence of the photo-production cross-section is being considered. We however find that the ratio of both cross-sections grows with energy in the presence of non-linear effects, while it remains approximately constant in the linearized case. The ratio of photo-production cross-sections might therefore provide a suitable tool to characterize the size of non-linear QCD effects at current collider energies.
 
 

Amplitudes of 3H, 3He Two-Particle Photo-Breakup in Non-Local QED Approach

Three-nucleon systems are essential for the investigation of many-body forces in nuclear physics. Well-grounded parametrization of their vertex functions with further application for the calculation of cross-sections in nonlocal QED approach provides the ground for investigation of the variety of multi-particle systems. In present paper we describe the process of parametrization of two-particle photo-breakup amplitudes of three-nucleon systems (3H, 3He). We provide the general description of the wave function construction for three-nucleon systems as well as the parametrization of their vertex functions accounting two- and three-nucleon interactions based on meson exchange current formalism. In our calculations we account first and second order one-pion exchange terms and the term related to the exchange of ω and ρ mesons. The three-nucleon interaction potential is given as a sum of attraction (two-pion exchange) term andappropriate repulsive part. Based on the variational ”Urbana + Model VII” amplitudes we provide the results for energy dependence of differential cross-section of 3He(γ, p)d reaction at proton angle θ = 90◦ from the threshold up to Eγ = 40 MeV and compare theoretical predictions with the available experimental data. The investigation is also provided for angular cross-section distributions at high photon energies (Eγ = 305 ± 5 MeV; 365 ± 5 MeV; 450 ± 10 MeV and 675 ± 50 MeV). Correct description of 3H, 3He photo-disintegration processes in a unified approach based on the gauge nature of the electromagnetic field implies application of this model for other multi-particle systems.

Spin-orbit charge transfer from guanine and 9-methylguanine radical cations to nitric oxide radicals and the induced triplet-to-singlet intersystem crossing.

Nitric oxide (●NO) participates in many biological activities, including enhancing DNA radiosensitivity in ionizing radiation-based radiotherapy. To help understand the radiosensitization of ●NO, we report reaction dynamics between ●NO and the radical cations of guanine (a 9HG●+ conformer) and 9-methylguanine (9MG●+). On the basis of the formation of 9HG●+ and 9MG●+ in the gas phase and the collisions of the radical cations with ●NO in a guided-ion beam mass spectrometer, the charge transfer reactions of 9HG●+ and 9MG●+ with ●NO were examined. For both reactions, the kinetic energy-dependent product ion cross sections revealed a threshold energy that is 0.24 (or 0.37) eV above the 0K product 9HG (or 9MG) + NO+ asymptote. To interrogate this abnormal threshold behavior, the reaction potential energy surface for [9MG + NO]+ was mapped out at closed-shell singlet, open-shell singlet, and triplet states using density functional and coupled cluster theories. The results showed that the charge transfer reaction requires the interaction of a triplet-state surface originating from a reactant-like precursor complex 3[9MG●+(↑)⋅(↑)●NO] with a closed-shell singlet-state surface evolving from a charge-transferred complex 1[9MG⋅NO+]. During the reaction, an electron is transferred from π∗(NO) to perpendicular π∗(9MG), which introduces a change in orbital angular momentum. The latter offsets the change in electron spin angular momentum and facilitates intersystem crossing. The reaction threshold in excess of the 0K thermochemistry and the low charge-transfer efficiency are rationalized by the vibrational excitation in the product ion NO+ and the kinetic shift arising from a long-lived triplet intermediate.

Enhanced Deuteron Coalescence Probability in Jets.

The transverse-momentum (p_{T}) spectra and coalescence parameters B_{2} of (anti)deuterons are measured in p-p collisions at sqrt[s]=13 TeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest p_{T} in the event (p_{T}^{lead}>5 GeV/c) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using pythia8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in pythia8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the B_{2}^{Jet} is not reproduced by the models, which instead give a decreasing trend.

Blazar boosted dark matter — direct detection constraints on σeχ : role of energy dependent cross sections

Elastic collisions with relativistic electrons from the blazar's jet can accelerate dark matter (DM) particles in the DM spike surrounding the supermassive black hole at its center. This can allow one to set stringent limits on the DM-electron scattering cross section (σ̅eχ ) for DM masses less than 100 MeV. We consider DM particles boosted by energetic electrons in the jets of the blazars TXS 0506+056 and BL Lacertae. Both vector and scalar mediators for the scattering of electron and electrophilic fermionic DM are studied. We highlight that the ensuing energy dependence of the S-matrix for the corresponding Lorentz structure of the vertex significantly modifies the constraints. We find that the revised exclusion limits are orders of magnitude stronger than the equivalent results for the simple constant cross section assumption. Our limits are also assessed for the less cuspy spike.

Bond Energies of UO+ and UC+: Guided Ion Beam and Quantum Chemical Studies of the Reactions of Uranium Cation with O2 and CO

AbstractGuided ion beam tandem mass spectrometry was used to examine the kinetic energy dependent reactions of U+ with O2 and CO. In the reaction of U+ with O2, the UO+ product is formed in a barrierless and exothermic process with a reaction efficiency at low energies of k/kcol=1.1±0.2, but increases at higher collision energies. Formation of both UO+ and UC+ in the reaction of U+ with CO is endothermic. 0 K bond dissociation energies (BDEs) of D0(U+‐O)=7.88±0.09 eV and D0(U+‐C)=4.03±0.13 eV were determined by analyzing the kinetic energy dependent cross sections in the latter endothermic reactions. These values are within experimental uncertainty of previously reported experimental values. Additionally, the electronic states of UO+ and UC+ and the potential energy surfaces for the reactions were explored by quantum chemical calculations. The former include a full Feller‐Peterson‐Dixon composite approach with correlation contributions up to CCSDT(Q) for UO and UO+, yielding D0(U‐O)=7.82 eV and D0(U+‐O)=7.99 eV, as well as more approximate CCSD(T) calculations where a semi‐empirical model was used to estimate spin‐orbit energy contributions, which are generally found to improve the agreement with experiment. Both experimental BDEs are observed to be close to those of their transition metal congeners, ScL+, YL+, and GdL+ (L=O and C).

Production cross sections of new neutron-rich isotopes with Z=92–106 in the multinucleon transfer reaction Au197+Th232

The multinucleon transfer reactions $^{197}\mathrm{Au}+^{232}\mathrm{Th}, ^{186}\mathrm{W}+^{232}\mathrm{Th}$, and $^{238}\mathrm{U}+^{232}\mathrm{Th}$ are investigated within the framework of dinuclear system (DNS) model with a decay model gemini$++$. The calculated isotopic production cross sections in the $^{136}\mathrm{Xe}+^{249}\mathrm{Cf}$ reaction at ${E}_{\mathrm{c}.\mathrm{m}.}=567\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ can reproduce the experimental data well. Due to the subshell closures, the behavior of ``inverse'' quasifission process is found in the collisions of $^{186}\mathrm{W}+^{232}\mathrm{Th}$ and $^{197}\mathrm{Au}+^{232}\mathrm{Th}$. The reaction $^{197}\mathrm{Au}+^{232}\mathrm{Th}$ is more advantageous to produce neutron-rich isotopes with $Z=92--106$ than $^{186}\mathrm{W}+^{232}\mathrm{Th}$ and $^{238}\mathrm{U}+^{232}\mathrm{Th}$, because it has the lowest value of the potential energy that needed to overcome in the nucleon transfer process. Furthermore, the incident energy dependence of isotopic production cross sections in the reaction $^{197}\mathrm{Au}+^{232}\mathrm{Th}$ is studied. It is found that ${E}_{\mathrm{c}.\mathrm{m}.}=756.47$ MeV is more suitable for producing new isotopes with $Z=92--98$, while ${E}_{\mathrm{c}.\mathrm{m}.}=690.69$ MeV is the optimal incident energy for $Z=99--106$. The effect of incident energy on the interaction time is also investigated. The production cross sections of 88 unknown neutron-rich transuranium nuclei are predicted with the cross sections at the order of ${10}^{\ensuremath{-}6}$ to $10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{b}$.

Thermochemistry of uranium sulfide cations: guided ion beam and theoretical studies of reactions of U+ and US+ with CS2 and collision-induced dissociation of US+

Reactions of atomic uranium cations with carbon disulfide form US+ in an efficient exothermic reaction and UCS+ in an inefficient endothermic process. The subsequent reaction of US+ with CS2 forms US2 + in an endothermic process having a low energy threshold. At much higher energies, UCS2 + and UCS+ are also formed. Collision-induced dissociation of US+ with Xe yields U+ + S exclusively in an endothermic reaction. Analysis of the kinetic energy dependent cross sections of the endothermic processes yields the 0 K bond dissociation energies of 5.73 ± 0.15 eV for U+ – S, 3.89 ± 0.08 eV for SU+ – S, 1.69 ± 0.17 eV for U+ – CS, 2.78 ± 0.33 eV for U+ – CS2, 1.53 ± 0.30 eV for SU+ – CS, and 5.65 ± 0.39 eV for S – UCS+. Theory is used to explore the structures and electron configurations of US+, US2 +, UCS+, and UCS2 +. The thermochemistry measured in this study is further compared to analogous values previously determined for select group 3 metals, lanthanides, and actinides.

Luminescence Measurements of the Hyperthermal Reactions of N/N+ + NH3.

Chemiluminescence from a system of collisions, N+/N/Kr+/Kr/Xe+/Xe + NH3, at collision energies between 10 and 170 eV (center of mass, COM), was measured in the spectral range 300-1000 nm. The energy dependence of the emission excitation cross sections was quantified, and molecular signatures were fit to known spectroscopic constants to determine vibrational-state populations. For both N and N+ collision species, the strongest features were assigned to emissions from NH (A-X) and the atomic hydrogen Balmer series. For each of the spectra resulting from collisions with primary cations, the NH (A-X) emissions had the largest cross sections reaching values of (1.0-1.5) × 10-18 cm2 by 100 eV. Additional features originating from atomic nitrogen and NH (c-a) emissions were also observed. The NH (c-a) emissions accounted for about 8%, 13%, and 15% for total excited populations in collisions with Xe+, N+, and Kr+, respectively. These transitions were consistent with short-range interactions resulting in collision-induced dissociation of the NH3 molecule with apparent energy thresholds between 20 and 30 eV and emission cross sections decreasing with ion mass. Evidence of charge exchange in the N+ + NH3 collisions was observed in the resulting spectra as broad transitions between 420 and 480 nm and were assigned to NH+ emitting from the (B) state. Differences between the spectra were observed as changes in the emission signal with the neutral collisions producing only 30% or 65% of the NH (A-X) emission cross sections compared to the cation results for xenon and krypton, respectively. For N and N+, NH (A) was created in equal amounts at lower collision energies, but the emission for the neutral system increases above that of the cation at collision energies greater than 80 eV COM. In both cases, the threshold energy for appearance was below 10 eV, suggesting an additional pathway for NH (A) formation, namely, hydrogen abstraction or charge exchange and abstraction for the N and N+, respectively. In all cases, the neutral NH (c-a) emission intensity was similar between neutral and cation pairs. The H-α emission line (n = 3-2) decreased to about 10%, 33%, and 50% of the corresponding cation spectra for xenon, krypton, and nitrogen, respectively.

Electron impact ionization in the icy Galilean satellites’ atmospheres

Electron impact ionization is critical in producing the ionospheres on many planetary bodies and, as discussed here, is critical for interpreting spacecraft and telescopic observations of the tenuous atmospheres of the icy Galilean satellites of Jupiter (Europa, Ganymede, and Callisto), which form an interesting planetary system. Fortunately, laboratory measurements, extrapolated by theoretical models, were developed and published over a number of years by K. Becker and colleagues (see Deutsch et al. in Adv At Mol Opt Phys 57:87–155, 2009) to provide accurate electron impact ionization cross sections for atoms and molecules, which are crucial to correctly interpret these measurements. Because of their relevance for the Jovian icy satellites, we provide useful fits to the complex, semiempirical Deutsch–Märk formula for energy-dependent electron impact ionization cross sections of gas-phase water products (i.e., H $$_2$$ O, H $$_2$$ , O $$_2$$ , H, O). These are then used with measurements of the thermal plasma in the Jovian magnetosphere to produce ionization rates for comparison with solar photo-ionization rates at the icy Galilean satellites.

Inclusive quarkonium production in pp collisions at sqrt{s} = 5.02 TeV

This article reports on the inclusive production cross section of several quarkonium states, textrm{J}/psi , psi mathrm{(2S)}, Upsilon mathrm (1S), Upsilon mathrm{(2S)}, and Upsilon mathrm{(3S)}, measured with the ALICE detector at the LHC, in pp collisions at sqrt{s} = 5.02 TeV. The analysis is performed in the dimuon decay channel at forward rapidity (2.5< y < 4). The integrated cross sections and transverse-momentum (p_{textrm{T}}) and rapidity (y) differential cross sections for textrm{J}/psi , psi mathrm{(2S)}, Upsilon mathrm (1S), and the psi mathrm{(2S)}-to-textrm{J}/psi cross section ratios are presented. The integrated cross sections, assuming unpolarized quarkonia, are: sigma _{textrm{J}/psi } (p_{textrm{T}} <20 GeV/c) = 5.88 ± 0.03 ± 0.34 ~mu b, sigma _{psi mathrm{(2S)}} (p_{textrm{T}} <12 GeV/c) = 0.87 ± 0.06 ± 0.10~mu b, sigma _{Upsilon mathrm (1S)} (p_{textrm{T}} <15 GeV/c) = 45.5 ± 3.9 ± 3.5 nb, sigma _{Upsilon mathrm{(2S)}} (p_{textrm{T}} <15 GeV/c) = 22.4 ± 3.2 ± 2.7 nb, and sigma _{Upsilon mathrm{(3S)}} (p_{textrm{T}} <15 GeV/c) = 4.9 ± 2.2 ± 1.0 nb, where the first (second) uncertainty is the statistical (systematic) one. For the first time, the cross sections of the three Upsilon states, as well as the psi mathrm{(2S)} one as a function of p_{textrm{T}} and y, are measured at sqrt{s} = 5.02 TeV at forward rapidity. These measurements also significantly extend the textrm{J}/psi p_{textrm{T}} reach and supersede previously published results. A comparison with ALICE measurements in pp collisions at sqrt{s} = 2.76, 7, 8, and 13 TeV is presented and the energy dependence of quarkonium production cross sections is discussed. Finally, the results are compared with the predictions from several production models.

Measurement of e+e− → ωπ+π− cross section at sqrt{s} = 2.000 to 3.080 GeV

A partial wave analysis on the process e+e− → ωπ+π− is performed using 647 pb−1 of data sample collected by using the BESIII detector operating at the BEPCII storage ring at center-of-mass (c.m.) energies from 2.000 GeV to 3.080 GeV. The Born cross section of the e+e− → ωπ+π− process is measured, with precision improved by a factor of 3 compared to that of previous studies. A structure near 2.25 GeV is observed in the energy-dependent cross sections of e+e− → ωπ+π− and ωπ0π0 with a statistical significance of 7.6σ, and its determined mass and width are 2232 ± 19 ± 27 MeV/c2 and 93 ± 53 ± 20 MeV, respectively, where the first and second uncertainties are statistical and systematic, respectively. By analyzing the cross sections of subprocesses e+e− → ωf0(500), ωf0(980), ωf0(1370), ωf2(1270), and b1(1235)π, a structure, with mass M = 2200 ± 11 ± 17 MeV/c2 and width Γ = 74 ± 20 ± 24 MeV, is observed with a combined statistical significance of 7.9σ. The measured resonance parameters will help to reveal the nature of vector states around 2.25 GeV.

Bounds on boosted dark matter from direct detection: The role of energy-dependent cross sections

The recoil threshold of Direct Detection experiments limits the mass range of Dark Matter (DM) particles that can be detected, with most DD experiments being blind to sub-MeV DM particles. However, these light DM particles can be boosted to very high energies via collisions with energetic Cosmic Ray electrons. This allows Dark Matter particles to induce detectable recoil in the target of Direct Detection experiments. We derive constraints on scattering cross section of DM and electron, using XENONnT and Super-Kamiokande data. Vector and scalar mediators are considered, in the heavy and light regimes. We discuss the importance of including energy dependent cross sections (due to specific Lorentz structure of the vertex) in our analysis, and show that the bounds can be significantly different than the results obtained assuming constant energy-independent cross-section, often assumed in the literature for simplicity. Our bounds are also compared with other astrophysical and cosmological constraints.

Zirconium Nuclear Data Campaign: Measurement of 90Zr (n, γ) cross section

The isotopes of Zr with A = [90, 91, 92, 94] make up more than 97% of naturally occurring Zr and are important to many nuclear applications such as nuclear reactors. One of the attractive qualities of naturally occurring Zr isotopes is that they have a low σγ/σt ratio at most neutron energies. Thus, they improve the neutron economy in reactors by preferentially scattering neutrons rather than absorbing them. This same quality also presents a challenge to measuring the capture cross section, σγ, of Zr isotopes. The ENDF/B-VIII.0 library has a relative uncertainty of approximately 10–20% for incident neutron energies &lt; 0.1 MeV and an uncertainty greater than 20% for energies &gt; 0.1 MeV for the majority of natural Zr isotopes. This motivated the Nuclear Criticality Safety Program to embark on a campaign to accurately measure and evaluate these Zr isotopes. In this work, we demonstrate energy-dependent neutron capture cross section measurements for the first enriched sample to be measured: 90Zr.

A quantum study of argon induced line mixing in ammonia doublets

We present a theoretical study of pressure broadening and coupling coefficients for selected doublets of the ν 4 band of ammomia in argon bath. Generalized spectroscopic kinetic energy dependent cross sections are determined quantum mechanically making use of available NH3-Ar potential energy surfaces. Thermally averaged values at various temperatures are also provided. Results are in overall good agreement with data available in the literature. A further study focusses on the speed dependence of the corresponding line shape parameters. The pressure broadening coefficients are found to have a well marked speed dependence while the intradoublet coupling terms show a small speed dependence at room temperature.