Multi-reference configuration interaction is used to produce potential energy curves (PECs) for the excited B1\Pi state of KH molecule. To investigate the correlation effect of core-valence electrons, five schemes are employed which include the different correlated electrons and different active spaces. The PECs are fitted into analytical potential energy functions (APEFs). The spectroscopic parameters, ro-vibrational levels, and transition frequencies are determined based on the APEFs and compared with available experimental and theoretical data. The molecular properties for B1| obtained in this letter, which are better than those available in literature, can be reproduced with calculations using the suitable correlated electrons and active space of orbitals.

We discuss the feasibility of realizing a cold atom space clock with counter-propagating cold atoms in microgravity. The design of the space clock is based on an atomic beam clock with Ramsey cavity, except that magneto-optical trap (MOT) is placed at each side. Cold atoms are launched simultaneously from the MOTs at both sides of the clock and they move at the counter-direction towards each other. The velocity of the launched atoms is precisely controlled to Ramsauer-Townsend resonance so that no additional collision frequency shift takes place. Such configuration can efficiently cancel the frequency shift resulting from cavity phase shift and increase the signal-to-noise ratio (SNR).

The Rb(5DJ)+H2 RbH+H photochemical reaction has been studied. Rb vapor mixed with H2 is irradiated in a glass cell with 778-nm pulses which populate one of the 5 2D states by two-photon absorption. Measurements for the relative intensities of the atomic fluorescence and the absorption of the RbH product near the axis of the cell yield the rate coefficients for the Rb(5D_{3/2})+H2 and Rb(5D_{5/2})+H2 reactions, which are (3.6\pm1.3)\times10^{-11} and (1.7\pm0.6)\times10^{-11} cm3/s, respectively. The relative reactivity with H2 for Rb(5D_{3/2}) is higher than that for Rb(5D_{5/2}).

The coupled equation method (CEM) has been applied to investigating the resonance structures for the ground state 1s2 2s 2S of the neutral lithium from the first threshold up to 64.5 eV. Resonance structures of atomic lithium due to single excitations of the 1s and 2s electrons are studied by infinite-order calculations in detail. The effect of spin-orbit splitting is also included for some of the low-lying 1s 2s np resonance, and the influence of the interference between 1s 2s 3S np and 1s 2s 1S np states on the resonance structure has been confirmed theoretically. The results show that the presented technique can give the reasonable resonance structures very well in photoionization processes.

We report experimentally the measured rate coefficients for the energy pooling (EP) collisions process Cs(5D)+Cs(5D)->Cs(6S)+Cs(nL=9D,11S,7F) in cesium densities of 10^(16)-10^(17) cm^(-3). The 5D state was populated via 8S->7P->5D spontaneous emission following two-step pumping 6S->6P_(3/2)->8S. Since the 5D->6P (3.0-3.6 microns) fluorescence could not be detected in this experiment, we carried out a relative measurement for the process 6P+5D->6S+7D. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode laser beam, tuned to 6P_(3/2)->9S_(1/2) transition, which could be translated parallelly to the pump beam. The excited atom densities have been combined with the measured fluorescence ratios to yield EP rate coefficients. The average values for nL=9D,11S and 7F are 8.0+-4.0, 7.0+-3.5, and 9.3+-4.6 (in units of 10^(-10) cm3/s), respectively. Influence of the energy transfer process 11S+6S->7F+6S on the rate coefficients k_(11S) and k_(7F) is also discussed.

Rate coefficients for energy-pooling (EP) collisions Rb(5P_(J))+Cs(6P_(3/2))-->Rb(5S_(1/2))+Cs(nl_(J')) have been measured. Atoms were excited to Rb(5P_(J)) and Cs(6P_(3/2)) states using two single-mode diode lasers. To isolate the heteronuclear contribution in the fluorescence spectrum, a double-modulation technique has been adopted. The excited-atom density and spatial distribution are mapped by monitoring the absorption of a counterpropagating single-mode diode laser beam, tuned to Rb(5P_(J)-->7S_(1/2)) and Cs(6P_(3/2)-->8S_(1/2)) transitions respectively, which could be translated parallelly to the pump beams. The excited atom densities are combined with the measured fluorescence ratios to determine cross sections for the EP processes. It was found that Rb(5P_(J))+Cs(6P_(3/2)) collisions are more efficient than Rb(5P_(3/2))+Cs(6P_(3/2)) collisions for populating Cs(4F_(5/2)), while the opposite is true for populating Cs(4F_(7/2)).

Using the optical-optical double resonance (OODR) technique, we have studied the collisional broadening of some 2^1Delta_g<--B^1Pi_u lines in Na2 molecules. A single line Ar+ laser is used to pump the sodium dimers from thermally populated ground state X^1Sigma+_g level to the intermediate B^1Pi_u state. Then, a single-mode diode laser is used to probe the doubly excited 2^1Delta_g state. The broadening rate coefficient is determined from the slope of the total linewidth versus Ne density curve. We obtain the average value k_(br)=(1.1+-0.5)*10^(-8) cm3/s. The collisional excitation transfer between rotational levels of the B^1Pi_u state (i.e., B^1Pi_u(2,83/84)<--B^1Pi_u(2,82)) is also investigated. The rates can be determined from the relative intensities of the main peak and satellite lines, combined with a rate equation model. The rates of 1.25*10^(6) and 1.07*10^(6) /s are obtained, respectively.

Considering the changes of the geometric shielding effect in a molecule as the incident electron energy varing, an empirical fraction, which is dependent on the incident electron energy, is presented. Using this empirical fraction, the total cross sections (TCSs) for electrons scattering from complex polyatomic molecules C2F4 and SO2 are calculated over a wide energy range from 30 to 5000 eV together with the additivity rule model at Hartree-Fock level. In the TCS calculations, the atoms are presented by the spherical complex optical potential, which is composed of static, exchange, polarization and absorption contributions. The quantitative TCSs above 100 eV are in good agreement with those obtained by experiments and other theories. It is proved that the empirical fraction, which exhibits the TCS contributions of shielded atoms in a molecule at different energies, is reasonable.