Low-energy nondipole effects in molecular nitrogen valence-shell photoionization

Observations are reported for the first time of significant nondipole effects in the photoionization of the outer-valence orbitals of diatomic molecules. Measured nondipole angular-distribution parameters for the 3sigma(g), 1pi(u), and 2sigma(u) shells of N2 exhibit spectral variations with incident photon energies from thresholds to approximately 200 eV which are attributed via concomitant calculations to particular final-state symmetry waves arising from (E1)multiply sign in circle(M1,E2) radiation-matter interactions first-order in photon momentum. Comparisons with previously reported K-edge studies in N2 verify linear scaling with photon momentum, accounting in part for the significantly enhanced nondipole behavior observed in inner-shell ionization at correspondingly higher momentum values in this molecule.     

钠分子B^1∏u与2^1∑g^＋间的碰撞激发转移

The B 1pi(u) electronic state of Na2 was excited by the 441.6 nm He-Cd laser line. The Na atomic transitions and the A 1sigma(u)+ --> X 1sigma(g)+ band of Na2 were recorded. From the intensities and spectra of the Na and Na2 fluorescence several collisional processes in the excited sodium atom-dimer system were identified. The Na atomic lines are the result of collisional energy transfer from Na2 (B 1pi(u)) to Na(3P). Predissociation process may also contribute to atomic fluorescence. The A 1sigma(u)+ --> X 1sigma(g)+ band is interpreted through a populating mechanism involving collisional transfer from B 1pi(u) to 2 1sigma(g)+ followed by a radiative transfer to the A 1sigma(u)+ state. From the decay constants and fluorescence intensities, the rate coefficient at 360 degrees C for collisional energy transfer from Na2 (B 1pi(u)) to Na2 (2 1sigma(g)+) was found to be 5.7 x 10(-10) cm3 x s(-1). The predissociation rate of the B 1pi(u) is 2.7 x 10(6) s(-1).     

锂分子3^1Ⅱg里德堡态的光谱研究

我们用脉冲光学-光学双共振荧光激发谱（OODR），测量了在35500-38000cm^-1能量范围内的里德堡态，观察到^7Li23^1Ⅱg态的10个振动能，本文观测的3^1Ⅱg态的146条激发谱线进行了归属，得到了新的Dunhm常数，RKR势能曲线以及A^1∑u^ 到3^1Ⅱg态跃迁的夫兰克-康登因子，并且讨论了3^1Ⅱg态的双重分裂以及与附近里德堡态F（4）^1∑g^ ,5^1∑g^ ,6^1∑g^ 和G（2）^1Ⅱg的微扰，发现在我们的实验精度下（0.2cm^-1)3^1Ⅱg态掇重分裂可以忽略。     

激光烧蚀Al热原子与CF4,CCl4,CH2Br2反应中激发态C2的形成

脉冲激光烧蚀平面铝靶产生的热原子与气相CF4,CCl4,CH2Br2的碰撞反应中,在430～600nm之间观测到激发态C2分子的发光光谱,它们可归属为Swan带的d^3Ⅱg=a^3Ⅱu跃迁中△v=2,1,0,-1,-2五个振动序列(v′≤6)。谱强度分析表明,C2激发态可很好的用热平衡描述,其振动温度达6000K左右。同时在△v=0和-1的振动带间观测到振荡的谱峰,它们是转动谱线叠加的结果。激光烧蚀Al产生的等离子体在膨胀中产生的激波及其本身的动能与反应气体碰撞使其解离产生C,然后复合形成C2。C2激发态d可能是通过激发态的Al(^2S)经近共振传能产生,也不排除在有足够碰撞能下优先形成C2激发态b,再通过与d态的v′=6能级交叉无辐射跃迁而进入d态。     

狭缝微放电等离子体参数的光谱测量

利用平行管水电极介质阻挡放电装置,在氩气和空气混合气体中,得到了狭缝微放电等离子体。利用发射光谱法,研究了此放电中分子振动温度、分子转动温度和电子的平均能量随气体压强的变化。通过氮分子第二正带系(C3Πu→B3Πg)的发射谱线计算了氮分子的振动温度;利用氮分子离子(N2+)的第一负带系(B2Σu+→X2Σg+)的发射谱线计算了氮分子的转动温度;测量了氮分子离子391.4 nm和激发态的氮分子337.1 nm两条发射谱线的相对强度之比,研究了电子能量的变化。结果表明,当压强从60 kPa增大到100kPa,分子振动温度及分子转动温度均减小,氮分子离子谱线与激发态的氮分子谱线的强度之比亦减小。     

利用发射光谱研究脉冲电晕放电中的自由基

利用发射光谱技术在大气压下测量了以氮气为载气的不饱和水蒸气体系针-板式正脉冲电晕放电产生的OH(A^2∑→X^2Ⅱ0—O)自由基和O(3p^5P→3s^5S^02777．4nm),Ha(3P→2S 656．3nm)活性原子的发射光谱,并由N2(C^3Ⅱu→B^3Ⅱg)的△v=-3和△v=-4振动带序发射光谱强度计算得出N2(C,v)的相对振动布居及其振动温度,进而采用高斯分布拟合准确地求出了N2(C^3Ⅱu→B^3Ⅱg)的△v= 1振动带序发射光谱强度,从而可以由N2(C^3Ⅱu→B^3Ⅱg)的△v= 1振动带序与OH(A^2∑→X^2Ⅱ0—0)的重叠发射光谱中准确求出OH(A^2∑→X^2Ⅱ0—0)自由基的发射光谱强度。由发射光谱强度得到了激发态OH(A^3∑)自由基和O(3p^5P),Ha(3P)活性原子的布居。还研究了激发态OH(A^2∑)自由基和O(3p^5P),Ha(3P)活性原子的布居随放电电压和放电频率的变化以及氧气对激发态OH(A^2∑)自由基和O(3p^5P),Ha(3P)活性原子布居的影响。     

Quantum criticality and minimal conductivity in graphene with long-range disorder

We consider the conductivity sigma of graphene with negligible intervalley scattering at half filling. We derive the effective field theory, which, for the case of a potential disorder, is a symplectic-class sigma model including a topological term with theta=pi. As a consequence, the system is at a quantum critical point with a universal value of the conductivity of the order of e(2)/h. When the effective time-reversal symmetry is broken, the symmetry class becomes unitary, and sigma acquires the value characteristic for the quantum Hall transition.     

Symmetry-resolved absorption spectra of vibrationally excited CO2 molecules

Symmetry-resolved x-ray absorption spectroscopy has been first carried out on high-temperature molecules. From the angle-resolved ion yield spectra of CO2 both at room temperature and at 430 degrees C, symmetry-resolved absorption profiles of the C 1s(-1) 2pi(u) and O 1s(-1) 2pi(u) resonances have been extracted for the vibrational ground state molecules and bending-vibration excited ones. The profiles change dramatically between them, and the Renner-Teller effect becomes more evident for the vibrationally excited molecules. The effects of the multimode vibronic coupling are suggested for the O 1s(-1) 2pi(u) and O 1s(-1) 3s sigma(g) resonances.     

光谱法研究低气压空气介质阻挡放电均匀性

利用介质阻挡放电装置.在低气压空气中得到了均匀放电,并采用光谱法,研究了放电等离子体温度的空间均匀性.实验采集了氮分子光谱,采用氮分子第二正带系C3Ⅱu→B3Ⅱg计算振动温度;采用氮分子离子第一负带系计算转动温度(气体温度).实验发现,振动温度随电压增加而减小,而转动温度随电压增加而增大.等离子体振动温度和转动温度在空...     

NO（D^2∑）共振增强的多光子离化谱

利用皮秒Nd：YAG激光器泵浦的光学参量发生傲大器作激发源，获得了NO分子在460～570nm波长范围内的多光子离化谱，测量了离化信号随激光强度的关系，其近五次方关系表明在460～570nm波长范围内NO分子吸收5个光子而离化。通过对谱线的归属，确认在此波长范围内，NO分子的离化过程是通过高激发态D^2∑的共振增强的多光子离化过程。用最小二乘法拟合，获得了D^2∑态的基振动频率和相互作用的力常数。     

Raman scattering from a superconductivity-induced bound state in MgB2

It is shown that the sharp peak in the E(2g) Raman spectrum of superconducting MgB2 is due to a bound state caused by the electron-phonon coupling. Our theory explains why this peak appears only in the spectra with E(2g) symmetry and only in the sigma but not the pi bands. The properties of the bound state and the Raman spectrum are investigated, also in the presence of impurity scattering.     

氩气含量对空气介质阻挡放电发射光谱的影响

利用介质阻挡放电实验系统测量了空气介质阻挡放电的发射光谱,研究了氩气含量对空气介质阻挡放电发射光谱的影响.在280～500 nm波长范嗣内,发现了氮分子第二正带系N2(C3∏u-B3∏g)的谱线和氮分子离子的第一负带系N2+(B3∑u+-X2∑g+)的谱线.在相同条件下加入10%氩气后,起始放电电压由26kV降低到23...     

Direct probe of the shape resonance mechanism in 2sigma(g)-shell photoionization of the N2 molecule

Angular distributions of photoelectrons from a 2sigma(g) shell of fixed-in-space N2 molecules have been measured for left- and right-elliptically polarized and for linearly polarized light at several photon energies in the region of sigma(*) shape resonance. That allowed the determination of a set of dipole matrix elements and phase shift differences characterizing the process. These data clearly show the enhancement of the fsigma(u) partial cross section in the resonance simultaneously with an abrupt increase of the corresponding phase shift by pi, which is the first experimental demonstration of the nature of the sigma(*) shape resonance in homonuclear diatomic molecules.     

Indication of a cosmological variation of the proton-electron mass ratio based on laboratory measurement and reanalysis of H2 spectra

Based on highly accurate laboratory measurements of Lyman bands of H2 and an updated representation of the structure of the ground X 1sigma(g)+ and excited B 1sigma(u)+ and C 1pi(u) states, a new set of sensitivity coefficients K(i) is derived for all lines in the H2 spectrum, representing the dependence of their transition wavelengths on a possible variation of the proton-electron mass ratio mu = m(p)/m(e). Included are local perturbation effects between B and C levels and adiabatic corrections. The new wavelengths and K(i) factors are used to compare with a recent set of highly accurate H2 spectral lines observed in the Q 0347-383 and Q 0405-443 quasars, yielding a fractional change in the mass ratio of deltamu/mu = (2.4 +/- 0.6) x 10(-5) for a weighted fit and deltamu/mu = (2.0 +/- 0.6) x 10(-5) for an unweighted fit. This result indicates, at a 3.5sigma confidence level, that mu could have decreased in the past 12 Gyr.     

Controlling high harmonic generation with molecular wave packets

We show that, by controlling the alignment of molecules, we can influence the high harmonic generation process. We observed strong intensity modulation and spectral shaping of high harmonics produced with a rotational wave packet in a low-density gas of N2 or O2. In N2, where the highest occupied molecular orbital (HOMO) has sigma(g) symmetry, the maximum signal occurs when the molecules are aligned along the laser polarization while the minimum occurs when it is perpendicular. In O2, where the HOMO has pi(g) symmetry, the harmonics are enhanced when the molecules are aligned around 45 degrees to the laser polarization. The symmetry of the molecular orbital can be read by harmonics. Molecular wave packets offer a means of shaping attosecond pulses.     

Measurement of the eta-meson mass using psi(2S) --> etaJ/psi

We measure the mass of the eta meson using psi(2S) --> etaJ/psi events acquired with the CLEO-c detector operating at the CESR e(+)e(-) collider. Using the four decay modes eta --> gamma gamma, 3pi(0), pi(+)pi(-)pi(0), and pi(+)pi(-)gamma, we find M(eta) = 547.785 +/- 0.017 +/- 0.057 MeV, in which the first uncertainty is statistical and the second systematic. This result has an uncertainty comparable to the two most precise previous measurements and is consistent with that of NA48, but is inconsistent at the level of 6.5 sigma with the much smaller mass obtained by GEM.     

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。     

The dynamics of spatiotemporal modulations

The modulational instability of traveling waves is often thought to be a crucial point in the mechanism of transition to space-time disorder and turbulence. The aim of this paper is to study the effect of spatiotemporal modulations on some dynamics u(0)(x,t), which may occur as an instability process when a control parameter varies, for instance. We analyze the properties of the modulated dynamics of the form g(1)(x)g(2)(t)u(0)(x,t) compared to those of the reference dynamics u(0)(x,t), using operator theory. We show that, if the reference dynamics is invariant under some space-time symmetry in the sense of Ref. [J. Nonlinear Sci. 2, 183 (1992)], the modulation has the effect of either deforming this symmetry or breaking it, depending on whether the corresponding operator remains unitary or not. We also demonstrate that the smallest Euclidean space containing the modulated dynamics has a dimension smaller than or equal to the smallest Euclidean space containing u(0)(x,t). The previous results are then applied to the case of modulated uniformly traveling waves. While the spatiotemporal translation invariance of the wave never persists in the presence of a modulation, the existence of a spatiotemporal symmetry depends on the resonance of the Fourier sidebands due to the modulation. In case of nonresonance, a spatiotemporal symmetry exists and is explicitly determined. In this situation, the modulated wave and the carrier wave have the same spectrum (up to a normalization factor), the same entropy, and the spatial (resp., temporal) two-point correlation is deformed only by the spatial (resp., temporal) modulation. (c) 1995 American Institute of Physics.     

Dynamic stabilization in 1sigma(u)-->1pi(g) excited nitrogen clusters

High-resolution 1s near-edge spectra of molecular nitrogen and variable size nitrogen clusters obtained using monochromatic synchrotron radiation from the high brilliance BESSY-II storage ring facility are reported. The vibrationally resolved 1sigma(u)-->1pi(g) core-to-valence excitation band of clusters shows a distinct redshift of 6+/-1 meV relative to the isolated molecule, but the vibrational structure and linewidths are essentially unchanged. This shift is assigned to dynamic stabilization of 1sigma(u)-->1pi(g) excited molecules in clusters, arising from the dynamic dipole moment generated by core-hole localization in the low-symmetry cluster field. This leads to changes in intermolecular interactions compared to the ground-state cluster. Such spectral shifts are expected to occur generally in molecular clusters and in the corresponding condensed phase.     

常压氩/氮射频容性放电冷等离子体的发射光谱诊断

实验中在大气压下在射频(13.56 MHz)容性耦合的平板形金属电极的构型中实现了氩/氮射频α模式的辉光放电.首先,采用发射光谱的方法测量了氮分子(C 3Ⅱu)谱线随氮气含量的变化;其次,使用玻耳兹曼斜率法估算了OH谱带(A2∑+→X 2Ⅱ)的转动温度,并得到等离子体温度随输入功率的变化规律.最后,选取氮的第二正带(C...