Observation of accurate ion dissociation thresholds in pulsed field ionization-photoelectron studies

We report the first observation, together with a mechanism for such an observation, of a steplike feature in the pulsed field ionization photoelectron measurement of CH4(C2H2), marking the 0 K dissociation threshold for the formation of CH3(+) + H(C2H(+) + H) from CH4(C2H2). The nonexistence of a step in the spectrum for C 2H4 at its dissociation threshold for C2H2(+) formation provides strong support for the proposed mechanism. This experiment shows that, for a range of molecules, where the ion dissociation lifetimes near the dissociation thresholds are <10(-7) s, pulsed field ionization photoelectron measurements will yield not only highly accurate ionization energies, but also 0 K dissociation thresholds.     

Transverse momentum and total cross section of e(+)e(-) pairs in the Z-boson region from p&pmacr; collisions at sqrt

The transverse momentum and total cross section of e(+)e(-) pairs in the Z-boson region of 66相似文献   

强激光场中H2^＋离解行为的研究

在多电子态模型下，利用二阶劈裂传播子算法计算了Ｈ２＾＋在强激光场中的离散行为。结果发现在高频场时分子的多光子离散碎片是近对称的，而对于低频场，在所考虑的激光强度下Ｈ２＾＋是被隧道离散的，因而其离散碎片Ｈ＾＋分布是反对称的，另外，文中还探讨了三脉冲形状对分子离解几率、离解碎片动力学行为的影响。     

Monochromatic soft-x-ray-induced reactions of CF2Cl2 adsorbed on Si(111)-7 × 7 studied by continuous-time photon-stimulated desorption spectroscopy near the F(1s) edge

Continuous-time core-level photon-stimulated desorption (PSD) spectroscopy was used to investigate the monochromatic soft x-ray photoreactions of CF(2)Cl(2) adsorbed on Si(111)-7 × 7 near the F(1s) edge (681-704 eV). Sequential F(+) PSD spectra were observed as a function of photon exposure at the CF(2)Cl(2)-covered surface (dose = 2.0 × 10(14) molecules cm(-2), ～0.75 monolayer). The F(+) PSD and total electron yield (TEY) spectra of solid CF(2)Cl(2) near the F(1s) edge were also measured. Both F(+) PSD and TEY spectra depict three features in the energy range of 687-695 eV, and are assigned to the excitations of F(1s) to (13a(1) + 9b(2))[(C-Cl)(?)], (7b(1) + 14a(1))[(C-F)?] antibonding and 5p Rydberg orbitals, respectively. Following the Auger decay process, two holes are created in the C-F bonding orbitals producing the 2h1e final state which results in the F(+) desorption. This PSD mechanism, responsible for the F(+) PSD of solid CF(2)Cl(2), is used to explain the first F(+) PSD spectrum in the sequential F(+) PSD spectra. The variation of spectral shapes in the sequential F(+) PSD spectra shows the consumption of adsorbed CF(2)Cl(2) molecules and the production of surface SiF species as a function of photon exposure. The photolysis cross section of the adsorbed CF(2)Cl(2) molecules by photons with varying energy (681-704 eV) is deduced from the sequential F(+) PSD spectra and found to be ～6.0 × 10(-18) cm(2).     

丁酮分子的多光子电离-离解机理

研究了丁酮分子经(n0,3d)共振的多光子电离-离解机理(MPID).多光子电离-飞行时间质谱测得的主要离子产物是C2H3O+和CH3CH+2,C2H3O+的强度为CH3CH+2的2～5倍,还有少量C2H+2,C2H+3和CH+3离子,未见到母体离子.主要离子产物的分质量多光了电离谱结构相似,而各离子产物的光强指数不同.实验结果说明丁酮分子的多光子电离-离解机理符合母体离子阶梯模型,文中用梯开关模型对主要产物离子的产生机理进行了解释.     

Symmetry breakdown in ground state dissociation of HD+

Experimental studies of the dissociation of the electronic ground state of HD+ following ionization of HD by fast proton impact indicate that the H++D(1s) dissociation channel is more likely than the H(1s)+D+ dissociation channel by about 7%. This isotopic symmetry breakdown is due to the finite nuclear mass correction to the Born-Oppenheimer approximation which makes the 1ssigma state 3.7 meV lower than the 2psigma state at the dissociation limit. The measured fractions of the two dissociation channels are in agreement with coupled-channels calculations of 1ssigma to 2psigma transitions.     

用可变阶数的代数方法研究双原子体系的完全振动能谱和离解能

不同双原子分子电子态的势能(或振动能谱)的展开性质可能不同,文章将固定阶数的代数方法(AM)改进为可变阶数的代数方法,使得该方法可以研究各种不同性质(不同能量展开阶数)的双原子分子电子态,也可以解决光谱计算中可能出现的"蝴蝶效应"问题。利用阶数可变的AM方法研究了原来固定阶数的AM方法难以给出正确结果的N2-a′1Σu-,Li2+-2 2Σg+,4 He D+-X1Σ+和39 K85 Rb-(2)3Σ+等不同双核体系的完全振动能谱与离解能,不但得到了与实验数据精确相符的理论结果,还正确地预言了许多由于实验条件与技术原因而未能测得的物理数据。研究表明阶数可变的AM方法能够更广泛地用于研究各类双核电子态体系的完全振动能谱和体系离解能。     

Electron spin resonance spectroscopy of molecules in large precessional motion: a case of H6(+) and H4D2(+) in solid parahydrogen

We have measured electron spin resonance (ESR) spectra of H6+ and H4D2(+) ions produced in gamma-ray irradiated solid parahydrogen. Anisotropic hyperfine-coupling constants for H6(+) and H4D2(+) determined by the analysis of ESR lines at 4.2K were -0.06 and -0.12 mT, respectively, which were opposite in sign to and much smaller than theoretical results of 1.17-1.25 mT. Although no change was observed in H6(+), the constant for H4D2(+) increased to be 1.17 mT at 1.7 K, which is very close to the theoretical value. We concluded that H6+ both at 4.2 and 1.7 K and H4D2(+) at 4.2K should be in a large precessional motion with the angle of 57-59 degrees, but the precession of H4D2(+) is stopped at 1.7 K.     

Indications of suppression of excited Υ states in Pb-Pb collisions at √(s(NN))=2.76 TeV

A comparison of the relative yields of Υ resonances in the μ(+)μ(-) decay channel in Pb-Pb and pp collisions at a center-of-mass energy per nucleon pair of 2.76 TeV is performed with data collected with the CMS detector at the LHC. Using muons of transverse momentum above 4 GeV/c and pseudorapidity below 2.4, the double ratio of the Υ(2S) and Υ(3S) excited states to the Υ(1S) ground state in Pb-Pb and pp collisions, [Υ(2S+3S)/Υ(1S)](Pb-Pb)/[Υ(2S+3S)/Υ(1S)](pp), is found to be 0.31(-0.15)(+0.19)(stat)±0.03(syst). The probability to obtain the measured value, or lower, if the true double ratio is unity, is calculated to be less than 1%.     

Rho0 production and possible modification in Au+Au and p+p collisions at square root [sNN] = 200 GeV

We report results on rho(770)(0)-->pi(+)pi(-) production at midrapidity in p+p and peripheral Au+Au collisions at sqrt[s(NN)]=200 GeV. This is the first direct measurement of rho(770)(0)-->pi(+)pi(-) in heavy-ion collisions. The measured rho(0) peak in the invariant mass distribution is shifted by approximately 40 MeV/c(2) in minimum bias p+p interactions and approximately 70 MeV/c(2) in peripheral Au+Au collisions. The rho(0) mass shift is dependent on transverse momentum and multiplicity. The modification of the rho(0) meson mass, width, and shape due to phase space and dynamical effects are discussed.     

Strong,polarized Balmer-alpha fluorescence after resonant core excitation of HCl

Visible-UV fluorescence has been analyzed after resonant Cl 2p core excitation of HCl molecules. The dispersed fluorescence spectra are dominated by emissions from atomic fragments. In particular, an intense and polarized Balmer H(alpha) line is observed after photoexcitation of the 2p(-1)nl Rydberg states. The excited hydrogen atoms are efficiently produced in the resonant Auger process and the subsequent dissociation of high lying HCl+ states. The experimental results, complemented by a time-resolved measurement of the H(alpha) decay, point to a universal mechanism for the production of H( n = 3) atoms in the dissociation of innershell excited HCl molecules.     

Determining the chirality of Yukawa couplings via single charged Higgs boson production in polarized photon collisions

When the charged Higgs boson is too heavy to be produced in pairs, the predominant production mechanism at linear colliders is via the single charged Higgs boson production processes, such as e(-)e(+)-->bcH+,taunuH+ and gammagamma-->bcH+,taunuH+. We show that the yield of a heavy charged Higgs boson at a gammagamma collider is typically 1 or 2 orders of magnitude larger than that at an e(-)e(+) collider. Furthermore, a polarized gammagamma collider can determine the chirality of the Yukawa couplings of fermions with charged Higgs boson via single charged Higgs boson production and, thus, discriminate models of new physics.     

Evidence for B+-->omegal+nu

We have searched for the decay B+-->omegal(+)nu (l=e or mu) in 78 fb(-1) of Upsilon(4S) data (85x10(6)BB events) accumulated with the Belle detector. The final state is fully reconstructed using the omega decay into pi(+)pi(-)pi(0), combined with detector hermeticity to estimate the neutrino momentum. A signal of 414+/-125 events is found in the data, corresponding to a branching fraction of (1.3+/-0.4+/-0.2+/-0.3)x10(-4), where the first two errors are statistical and systematic, respectively. The third error reflects the estimated form-factor uncertainty.     

四氟化碳分子电离解离过程中的异构化动力学

采用离子动量成像谱仪研究了能量为1.0 ke V的电子束碰撞条件下CF₄分子的解离动力学.实验上,对解离离子的三维动量进行了成像测量,通过离子飞行时间关联谱识别了CF₄²⁺异构化生成F₂⁺分子的两个通道:F₂⁺+CF₂⁺与CF⁺+F₂⁺+F,得到了两个通道的离子动能及动能释放分布.对于其中的三体解离通道,我们进一步采用Dalitz图与Newton图等三体动力学分析方法对解离碎片的动量关联进行了分析.该通道以两个带电离子的背对背出射为主,中性的F原子作为旁观者只得到极小的反冲动量.     

Three-body dissociation dynamics of the low-lying Rydberg states of H3 and D3

The dynamics of the three-body dissociative charge exchange of fast (12 keV) H+3 and D+3 with Cs have been studied using multiparticle translational spectroscopy. The observed partitioning of product momenta was found to be state-specific and yields insights into the nuclear motion during dissociation for the three lowest-lying 2s 2A'1, 2p 2A'2, and 3p 2E' metastable Rydberg states of H3 and the 2s 2A'1 and 2p 2A'2 states for D3. These results provide direct empirical information on the nonadiabatic couplings that govern the three-body dissociation of the lowest-lying Rydberg states of H3 and D3.     

First direct measurement of the parity-violating coupling of the Z0 to the s quark

We present the first direct measurement of A(s), the parity-violating coupling of the Z0 boson to the strange quark, using approximately 550 000 e(+)e(-)-->Z0-->hadrons events recorded by the SLC Large Detector with a polarized e(-) beam. We tagged Z0-->s&smacr; events by the absence of B or D hadrons and the presence in each hemisphere of a high momentum K+/- or K(0)(s). Fitting the polar angle distributions of the strangeness-signed thrust axis gave A(s) = 0.895+/-0.066(stat)+/-0.062(syst). The analyzing power and uu+d&dmacr; background were constrained using the data, greatly reducing any model dependence.     

e+ e- annihilation into J/psi + J/psi

Recent measurements by the Belle Collaboration of the exclusive production of two charmonia in e(+)e(-) annihilation differ substantially from theoretical predictions. We suggest that a significant part of the discrepancy can be explained by the process e(+)e(-)-->J/psi+J/psi. Because the J/psi+J/psi production process can proceed through fragmentation of two virtual photons into two cc pairs, its cross section may be larger than that for J/psi+eta(c) by about a factor of 3.7, in spite of a suppression factor alpha(2)/alpha(2)(s) that is associated with the QED and QCD coupling constants.     

Stimulated desorption of cations from pristine and acidic low-temperature water ice surfaces

Electron-impact ionization of low-temperature water ice leads to H+, H+2, and H+(H2O)(n=1-8) desorption. The 22 eV H+ desorption threshold is correlated with localized 2-hole 1-electron and 2-hole final states which Coulomb explode, while the 22 eV H+2 threshold is due to H2O+ unimolecular dissociation. The 70 eV primary cluster ion threshold is consistent with holes in the 2a(1) level and secondary ionization channels. All cation yields are sensitive to local structural changes and probe surface acidity. The cluster size distribution indicates hole-hole screening distances of 1-2 nm.     

Hunting for glueballs in electron-positron annihilation

We calculate the cross section for the exclusive production of J(PC)=0(++) glueballs G0 in association with the J/psi in e(+)e(-) annihilation using the perturbative QCD factorization formalism. The required long-distance matrix element for the glueball is bounded by CUSB data from a search for resonances in radiative Upsilon decay. The cross section for e(+)e(-)-->J/psi+G0 at sqrt[s]=10.6 GeV is similar to exclusive charmonium-pair production e(+)e(-)-->J/psi+h for h=eta(c) and chi(c0), and is larger by a factor of 2 than that for h=eta(c)(2S). As the subprocesses gamma(*)-->(cc)(cc) and gamma(*)-->(cc)(gg) are of the same nominal order in perturbative QCD, it is possible that some portion of the anomalously large signal observed by Belle in e(+)e(-)-->J/psiX may actually be due to the production of charmonium-glueball J/psiG(J) pairs.     

Search for X(3872) in gammagamma fusion and radiative production at CLEO

We report on a search for the recently reported X(3872) state using 15.1 fb(-1) of e(+)e(-) data taken in the sqrt[s] = 9.46-11.30 GeV region. Separate searches for the production of the X(3872) in untagged gammagamma fusion and e(+)e(-) annihilation following initial state radiation are made by taking advantage of the unique angular correlation between the leptons from the decay J/psi --> l(+)l(-) in X(3872) decay to pi(+)pi(-)J/psi. No signals are observed in either case, and 90% confidence upper limits are established as (2J+1)Gamma(gammagamma)(X(3872))B(X --> pi(+)pi(-)J/psi) < 12.9 eV and Gamma(ee)(X(3872))B(X- -> pi(+)pi(-)J/psi) < 8.3 eV.