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。     

Resonance-enhanced multiphoton ionization of NO via X2П→A2∑ transition

The resonance-enhanced multiphoton ionization (REMPI) spectrum of NO has been obtained in the range of 420-480 nm with a Nd:YAG pumped optical parametric generator and amplifier. The spectral linescan be attributed to NO X2П(v" = 0, 1) → A2∑(v' = 0, 1) transitions. In this wavelength range, NO molecules are ionized via the resonant intermediate state A2∑+ and by a (2 + 2) REMPI process. The dependence of ion signals on laser intensity and gas pressure is discussed. The variation of the ionization signal versus laser intensity is near quartic. This is in good agreement with theory.     

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of the Cl and Cl isotopomers of p-chloroanisole

The geometric structures and vibrations of p-chloroanisole isotopomers in the first electronically excited state were studied by mass-analyzed resonance-enhanced two-photon ionization spectroscopy and by theoretical calculations. The band origins of the S₁ ← S₀ electronic transitions of ³⁵Cl and ³⁷Cl isotopomers were found to be equivalent at 34 859 ± 3 cm⁻¹. Assignments of the observed vibrational bands of the two isotopomers were made mainly based on the CIS/cc-PVDZ calculations and on conformity with the available data in the literature. Although the general spectral features of these two isotopomers are similar, the frequencies of some vibrational modes are different. This frequency shift partially depends on the degree of involvement of the chlorine atom in the molecular vibrations.     

Resonance enhanced multiphoton ionization (REMPI) and REMPI-photoelectron spectroscopy of ammonia

Resonance enhanced multiphoton ionization (REMPI) spectroscopy, preferably linked with kinetic energy analysis of the resulting photoelectrons (REMPI-photoelectron spectroscopy (PES)), continues to make enormous contributions to our understanding of the spectroscopy and, in many cases, the decay dynamics of small molecules in excited (normally Rydberg) electronic states. Here we present results of recent REMPI and REMPI-PES studies involving the ammonia molecule which provide further illustration of some of the many opportunities offered by these techniques. Received: 28 January 1998 / Revised: 3 April 1998 / Accepted: 15 April 1998     

CP-sensitive observables in e^ + e^-\to\tilde\chi^0_i \tilde\chi^0_j and neutralino decay into the Z boson

We study CP-sensitive observables in the neutralino production and the subsequent two-body decays of the neutralino and of the Z boson . We identify the CP-odd elements of the Z boson density matrix and propose CP-sensitive triple-product asymmetries. We calculate these observables and the cross sections in the minimal supersymmetric standard model with complex parameters and M ₁ for an e ⁺ e ^- linear collider with GeV and longitudinally polarized beams. We show that the asymmetries can reach for and for and discuss the feasibility of measuring these asymmetries.Received: 4 February 2004, Revised: 17 May 2004, Published online: 2 July 2004     

Localized and dispersive states in the multiphoton ionization processes

We introduce the notion of localized and dispersive states in the problem of multiphoton ionization of atoms by a laser beam. The connection is made with the ionization probability.     

Reconstruction of $$ \tilde \tau _1 $$ mass at the LHC

The cascade mass reconstruction approach was used for mass reconstruction of the lightest $ \tilde \tau $ \tilde \tau produced at the LHC in the cascade decay $ \tilde g \to \tilde bb \to \tilde \chi _2^0 bb \to \tilde \tau _1 \tau bb \to \tilde \chi _1^0 \tau \tau bb $ \tilde g \to \tilde bb \to \tilde \chi _2^0 bb \to \tilde \tau _1 \tau bb \to \tilde \chi _1^0 \tau \tau bb . The $ \tilde \tau _1 $ \tilde \tau _1 mass was reconstructed assuming that masses of gluino, bottom squark, and two lightest neutralinos were reconstructed in advance. SUSY data sample sets for the SU(3) model point containing 160k events each were generated which corresponded to an integrated luminosity of about 8 fb⁻¹ at 14 TeV. These events were passed through the AcerDET detector simulator, which parametrized the response of a generic LHC detector. The mass of the $ \tilde \tau _1 $ \tilde \tau _1 was reconstructed with a precision of about 20% on average.     

(2 + 1) Resonance enhanced multiphoton ionization of hydrogen chloride in a pulsed supersonic jet: Vacuum wavenumbers of rotational lines with detailed band analysis for excited electronic states of HCl

A comprehensive study of the excited electronic states of HCl is reported. Using resonance enhanced multiphoton ionization ((2 + 1) REMPI) and time-of-flight mass spectrometry (TOFMS) over 120 band systems are analyzed. Supersonic jet techniques are used to prepare rotationally cold species for laser spectroscopy in the 77 000 to 96 000 cm⁻¹ region. At least 50 new electronic states are characterized as well as several features only tentatively assigned previously. A long vibrational progression consisting of 29 vibrational levels of the deeply bound V¹Σ⁺(0⁺) valence/ion-pair state is studied. We also extend the identification and analysis to high vibrational levels of low-lying Rydberg states. The assignments of [²Π_i] Rydberg state complexes are evaluated in terms of spin-orbit coupling and united-atom calculations. In several band systems, the spectra exhibit anomalous rotational line intensities and broadened linewidths which are consistent with predissociation. Multiphoton ionization with mass spectrometry permits the investigation of isotope effects as well as the appearance of fragment species associated with repulsive potential curves.     

Calculation ofn^3 S_1 (Q\bar Q) \to \gamma + (pseudo)scalar

The decays of³ S ₁ quarkonia into a photon and a scalar or pseudoscalar Higgs particle are examined, taking into account the bound-state dynamics in the framework of a nonrelativistic potential model. We find that for realistic quark potentials the naive calculation [1] overestimates the scalar rate. Numerical results are obtained for the \(\bar bb\) and \(\bar tt\) quark systems.     

Photoelectron imaging of resonance-enhanced multiphoton ionization and above-threshold ionization of ammonia molecules in a strong 800-nm laser pulse

In this work, we mainly investigate the NH3 molecular multiphoton ionization process by using the photoelectron velocity map imaging technique. Under the condition of femtosecond laser(wavelength at 800 nm), the photoelectron images are detected. The channel switching and above-threshold ionization(ATI) effect are also confirmed. The kinetic energy spectrum(KES) and the photoelectron angular distributions(PADs) are obtained through the anti-Abel transformation from the original images, and then three ionization channels are confirmed successfully according to the Freeman resonance effect in a relatively low laser intensity region. In the excitation process, the intermediate resonance Rydberg states are C~(~(～1)) A _1(6 + 2 photons process), B~(～1) E(6 + 2 photons process) and C~(～1) A _1(7 + 2 photons process), respectively. At the same time, we also find that the photoelectron angular distributions are independent of laser intensity. In addition, the electrons produced by different processes interfere with each other and they can produce a spider-like structure. We also find ac-Stark movement according to the Stark-shift-induced resonance effect when the laser intensity is relatively high.     

\hat sl(2) \oplus \hat sl(2)/\hat sl(2) coset theory is a Hamiltonian reduction of the \hat D(2|1;\alpha ) superalgebra

It is shown that $\hat sl(2)_{k_1 } \oplus \hat sl(2)_{k_2 } /\hat sl(2)_{k_1 + k_2 } $ coset theory is a quantum Hamiltonian reduction of the exceptional affine Lie superalgebra $\hat D(2|1;\alpha )$ . In addition, the W algebra of this theory is the commutant of the U _q D(2|1;a) quantum group.     

Radiative decay of doubly excited states in helium below the He+ (N = 2) ionization threshold

The radiative decay of (1)P(o) doubly excited states in helium has been investigated using a novel apparatus in which metastable atoms and vacuum ultraviolet photons are detected. The intensity ratio of the energetically narrow (sp,2n-)(1)P(o) and (2p,nd)(1)P(o) series to the broader (sp,2n+)(1)P(o) series is strikingly enhanced in comparison with conventional photoabsorption, photoion, or photoelectron measurements using synchrotron radiation. The experimental approach is a new way forward for the study of energetically narrow doubly excited states.     

电子碰撞He(1s2)原子电离的初态依赖与角度关联的无关性

利用DS3C模型,考虑了入射道靶原子He基态几种不同关联形式的波函数 ,分别计算了He(1s2)(e,2e)反应的三重微分截面.结果表明,微分截面的角度分布与靶基态任何形式的关联无关,而主要取决于出射道粒子间的干涉、关联、交换和多体耦合的共同作用.     

NO2分子的光学-光学双色双共振多光子离化谱

以Nd:YAG激光器的二倍频输出光为抽运光,其三倍频输出抽运的光学参量发生/放大器输出光为探测光,利用光学-光学双色双共振多光子离化光谱技术(OODR-MPI),获得了NO2分子在605-675 nm探测光波长范围内的多光子离化激发谱.通过对NO2分子离化机理的分析,确定了在此波长区间,NO2分子经1 3 1双共振多光子过程离化,离化通道为NO2(X2 A1)→hv1NO2(A2 B2)→3hv2NO2(3pσu)→hv2NO2 e.谱线归属结果表明,所得OODR-MPI谱对应于NO2分子3p%里德伯态的三光子共振吸收,获得了该态的对称伸缩振动频率ω1=(1442.5±25.5)cm-1,弯曲振动频率ω2=(590.5±4.9)cm-1,其带源位于(58331±71)cm-1处,量子亏损值为0.69.     

A theoretical study of the lowest 2 B 1, 2 A 1 and 2 B 2 electronic states in H2S+ and a comparison with corresponding states in related systems

Large scale configuration interaction calculations are employed to study the potential energy surfaces of the three lowest lying states in H₂S⁺. The calculated structural data for the X ² B ₁ and A ² A ₁ states are in very good agreement with previous evidence, but the ² B ₂ state is found to exhibit an [S---H₂]⁺ structure with large SH bond separations and a very small internuclear angle of 32°. Energies and wavefunctions are calculated for all three vibrational modes in the X ² B ₁ and A ² A ₁ excited states of H₂S⁺ and D₂S⁺ and the corresponding Franck-Condon factors for the A ² A ₁-X ² B ₁ band are determined; a maximum in absorption intensity is predicted to occur for v′₂ = 5–6 in H₂S⁺ and for v′₂ = 7–8 in D₂S⁺ for the A ² A ₁-X ² B ₁ transition, for which the calculated T ₀ energy of 18 620 cm^-1 is in excellent agreement with the experimentally determined value of 18 520 cm^-1. Extensive comparison is made with the other AH₂ systems PH₂, NH₂ and H₂O⁺ and trends with respect to geometry, vertical excitation and ionization energies as well as vibrational structure are pointed out; for this purpose the ² B ₂ potential energy curve of PH₂ has also been calculated.     

Dissociation energies of the I(3/2g) and I(1/2g) states of Ar+ 2

Rotationally resolved pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectra of ⁴⁰Ar₂ and ³⁶Ar₂ have been recorded between 124650cm^?1 and 127 150cm^?1 following resonant two-photon excitation via the 0⁺ _u (v¹= 0) Rydberg state located below the Ar (¹S₀) + Ar?((3p)⁵4s′ [1/2]₁) dissociation limit. Four overlapping vibrational progressions were observed and attributed to transitions to the I(1/2u) u⁺ = 35–50, I(3/2g) u⁺ = 0–10, I(1/2g) v⁺ = 0–6 and I(3/2u) v⁺ = 0–2 vibronic states of Ar⁺ ₂. The vibrational quantum numbers of the ionic states were derived from an analysis of the isotopic shifts, and the dissociation energies of the I(3/2g) (D⁺ ₀(⁴⁰Ar⁺ ₂:) = 1509.4 ± 1.2cm^?1) and the I(1/2g) (D⁺ ₀(⁴⁰Ar⁺ ₂) = 616.3 ± 1.2cm^?1) states were determined.     

High resolution multiphoton ionization and dissociation of acetone via $\mathsf{3s\leftarrow n}$ Rydberg transitions

Measurements of multiphoton ionization and dissociation of acetone are reported in the wavelength range 582.60-585.80 nm at photon energy resolution of 0.3 cm^-1. To our knowledge there are not available results of (3 + 2) REMPI on acetone at 0.01 nm in this region. The experiments were performed using an Nd: YAG-OPO (optical parametric oscillator) laser system coupled to time-of-flight mass spectrometer. The ion yield and the single ion channel are presented. The high-resolution three-photon resonance multiphoton spectrum of the acetone Rydberg transition is also reported. The experimental results show three dissociation channels of the acetone ion, leading to the products: (CH₃CO ⁺ ), (CH₃ ⁺ ) and (COH ⁺ ); the channel CH₃COCH ₃CO ⁺ + CH₃ being the most favored. The acetone and acetyl ions are observed in all wavelength range investigated. In addition, we have measured the origin of the and transitions, and vibrational bands of the 3s state.Received: 21 March 2004, Published online: 11 May 2004PACS: 33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 33.15.Ta Mass spectra - 33.80.Gj Diffuse spectra; predissociation, photodissociation