On constructing the wave function of a quantum particle from its Wigner phase-space distribution function

For a Schrödinger wave function, the part of the phase that depends only on time disappears in the construction of the corresponding Wigner phase-space (quasi)distribution function. Despite this, it can be recovered from the Wigner function using the quantum Hamilton–Jacobi equation. This is demonstrated for three simple cases.     

Electron impact induced fluorescence of dissociating fragments from jet-cooled methane,methanol and ethanol

Dissociation fragments, following 20 keV electron impact on supersonic jet targets of methane, methanol and ethanol, have been analysed to determine rotational temperatures. The intensities of individual rotational lines of the CH A² Δ-X²Π, CH B²∑^- -X²Π and CH⁺A¹ Π-X¹∑⁺ transitions were measured and fitted to Boltzmann distributions. The temperatures obtained were about 4000 K for the CH A-X, 2000 K for the B-X and 1650 K for the CH⁺A-X transitions. The recorded spectra showed distributions at single temperatures. The intensities were also fitted to theoretical distributions in order to obtain excess energies. Possible fragmentation mechanisms are discussed.     

Attosecond strobing of two-surface population dynamics in dissociating H2+

Using H2+ and D2+, we observe two-surface population dynamics by measuring the kinetic energy of the correlated ions that are created when H2+ (D2+) ionize in short (40-140 fs) and intense (10(14) W/cm2) infrared laser pulses. Experimentally, we find a modulation of the kinetic energy spectrum of the correlated fragments. The spectral progression arises from a hitherto unexpected spatial modulation on the excited state population, revealed by Coulomb explosion. By solving the two-level time-dependent Schr?dinger equation, we show that an interference between the net-two-photon and the one-photon transition creates localized electrons which subsequently ionize.     

Exact non-Born-Oppenheimer wave function for the Hooke-Calogero model of the H2 molecule

The Hooke-Calogero model of the H₂ molecule, a four body system consisting of two protons and two electrons with harmonic electron-nuclear, Coulombic electron-electron and inverse quadratic nuclear-nuclear interactions, has been analyzed in–depth. A fully analytical closed–form non-Born-Oppenheimer solution has been found and based on it the properties of both electron–pair and nuclear–pair densities have been studied. Nuclei have been found to be strongly correlated in a way that resembles a sort of Wigner crystallization, for moderate electron–nucleus confinement strengths. Additionally, we have explicitly evaluated the Coulomb holes for the electrons. Analysis of these holes reveals that the similarity between the electron correlation effects of the model as compared to the real Coulombic systems is remarkable.     

Imaging and control of interfering wave packets in a dissociating molecule

Using two identical 110 femtosecond (fs) optical pulses separated by 310 fs, we launch two dissociative wave packets in I2. We measure the square of the wave function as a function of both the internuclear separation, /Psi(R)/(2), and of the internuclear velocity, /Psi(v(R))/(2), by ionizing the dissociating molecule with an intense 20 fs probe pulse. Strong interference is observed in both /Psi(R)/(2) and in /Psi(v(R))/(2). The interference, and therefore the shape of the wave function, is controlled through the phase difference between the two dissociation pulses in good agreement with calculations.     

Spatial imaging of the H2(+) vibrational wave function at the quantum limit

We experimentally obtained a direct image of the nuclear wave functions of H(2)(+) by dissociating the molecule via electron attachment and determining the vibrational state using the cold target recoil ion momentum spectroscopy technique. Our experiment visualizes the nodal structure of different vibrational states. We compare our results to the widely used reflection approximation and to quantum simulations and discuss the limits of position measurements in molecules imposed by the uncertainty principle.     

Neutron velocity distribution from a superthermal solid 2H2 ultracold neutron source

We have determined for the first time the velocity distribution of neutrons from a solid ²H₂ ultracold neutron (UCN) source. The spectrum rises sharply above 4.5m/s and has a maximum around 7m/s after transport in an 8m long guide. The number of neutrons in the UCN velocity range (< 7m/s) may be increased by a factor of two by placing the experiment 1m above the UCN source level.     

Suppression of the plasma oscillation by a wave perturbation on the beam distribution function

The suppression of naturally excited waves by an externally applied wave in the travelling wave type of beam-plasma interaction is shown to be due to a wave perturbation on the beam distribution function experimentally.     

A wave function for the H center in LiF

A wave function for the H center in LiF is proposed, assuming a linear combination of appropriate molecular orbitals. The fitting of theoretical calculations for the hyperfine constants with experimental results shows that the proposed wave function can represent well this defect.     

Characteristic features of the formation of the vibrational distribution function of H2 molecules in a hydrogen stream

A theoretical analysis is made of the flow of vibrationally excited hydrogen in a channel. It is shown that coverage of the channel walls with adsorbed hydrogen atoms can substantially increase the concentration of vibrationally excited molecules in the stream. The possibility of applying these results to bulk sources of negative H⁻ hydrogen ions is discussed. It is shown that the rate of H⁻ ion generation in the source may be enhanced appreciably under conditions where this generation is achieved by dissociative attachment of thermal electrons to H₂ molecules injected into the discharge chamber, whose vibrational distribution function has been pre-enriched in excited molecules by suitably organizing the hydrogen flow in the channel. Zh. Tekh. Fiz. 69, 15–21 (June 1999)     

Determination of shock wave velocity from photographs obtained using a polarization interferometer

A polarization shear interferometer is described in which one of the two images of the flow being studied is produced outside the interference field and serves as a shadow pattern. This image is recorded again using an additional light source — a pulsed laser. In this way one can determine the shock wave velocity and establish, on the basis of gas-dynamic relationships, the proper numeration of the interference fringes on the interferogram.     

Vibrational spectra obtained from high quality potential energy surfaces spanned by low level normal coordinates: application to CHFClI and CDFClI

The impact of approximate normal coordinates for spanning high level potential energy surfaces on vibrational frequencies is studied within the framework of vibrational SCF and configuration interaction calculations (VCI). The use of low level normal coordinates avoids expensive geometry optimizations and harmonic frequency calculations and thus allows for a significant reduction in CPU time. Benchmark calculations are provided for a set of molecules ranging from 5 to 7 atoms. An application to CHFClI and CDFClI shows that this approximation still allows for very accurate results. These molecules are of particular interest for studying parity violation effects.     

Vibrational pumping of H2 molecules in a hydrogen stream flowing through a cesium-hydrogen discharge

The H₂ molecular vibrational distribution function that is formed in a flow of molecular hydrogen is calculated. It is assumed that the hydrogen stream flows in a planar channel and passes through two sections in succession. In the first section a cesium-hydrogen discharge and preliminary vibrational pumping of H₂ molecules occur. In the second section, where there is no discharge, the v-v exchange process results in a considerable increase in the density of vibrationally excited molecules in a certain upper part of the vibrational spectrum. The possibility of using the vibrational distribution function produced in this manner to generate negative hydrogen ions as a result of subsequent dissociative attachment of electrons to vibrationally excited molecules is discussed. Zh. Tekh. Fiz. 68, 10–19 (October 1998)     

Ar2H+ 分子振动光谱的理论计算

基于近期由本组提供的Ar2 H+ 分子的基态势能面 ,应用含时波包演化方法 ,计算了总角动量J =0时的振动光谱 ,并对其中的一些谱峰进行了指认 .与现有的abinitio结果进行比较 ,这个新势能面包含了关于Ar2 H+ 基态的比较正确的信息     

Interference of dissociating wave packets in the I2 molecule driven by femtosecond laser pulses

The interference between two dissociating wave packets of the I2 molecule driven by femtosecond laser pulses is theoretically studied by using the time-dependent quantum wave packet method.Both the internuclear distanceand velocity-dependent density functions are calculated and discussed.It is demonstrated that the interference pattern is determined by the phase difference and the delay time between two pump pulses.With two identical pulses with a delay time of 305 fs and a FWHM of 20 fs,more interference fringes can be observed,while with two pump pulses with a delay time of 80 fs and a FWHM of 20 fs,only a few interference fringes can be observed.