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Zong-Chao Yan

Publications and source records attributed to Zong-Chao Yan.

31 records · Page 2Linked to original sources
arXiv2012

Precision spectroscopy of the hydrogen molecular ions HD$^+$

Expectation values of the Breit operators and the $Q$ terms are calculated for HD$^+$ with the vibrational number $v=0-4$ and the total angular momentum $L=0-4$. Relativistic and radiative corrections to some ro-vibrational transition frequencies are determined. Numerical uncertainty in $R_{\infty}α^2$ order correction is reduced to sub kHz or smaller. Our work provides an independent verification of Korobov's calculations [Phys. Rev. A {\bf74}, 052506 (2006); {\bf77}, 022509 (2008)].

physics.atom-ph↗
arXiv2012

The long-range non-additive three-body dispersion interactions for the rare gases, alkali and alkaline-earth atoms

The long-range non-additive three-body dispersion interaction coefficients $Z_{111}$, $Z_{112}$, $Z_{113}$, and $Z_{122}$ are computed for many atomic combinations using standard expressions. The atoms considered include hydrogen, the rare gases, the alkali atoms (up to Rb) and the alkaline-earth atoms (up to Sr). The term $Z_{111}$, arising from three mutual dipole interactions is known as the Axilrod-Teller-Muto coefficient or the DDD (dipole-dipole-dipole) coefficient. Similarly, the terms $Z_{112}$, $Z_{113}$, and $Z_{122}$ arise from the mutual combinations of dipole (1), quadrupole (2), and octupole (3) interactions between atoms and they are sometimes known, respectively, as DDQ, DDO, and DQQ coefficients. Results for the four $Z$ coefficients are given for the homonuclear trimers, for the trimers involving two like-rare-gas atoms, and for the trimers with all combinations of the H, He, Li atoms. An exhaustive compilation of all coefficients between all possible atomic combinations is presented as supplementary data.

physics.atom-ph↗
arXiv2010

Sensitive frequency-dependence of the carrier-envelope phase effect on bound-bound transition: an interference perspective

We investigate numerically with Hylleraas coordinates the frequency dependence of the carrier-envelope phase (CEP) effect on bound-bound transitions of helium induced by an ultrashort laser pulse of few cycles. We find that the CEP effect is very sensitive to the carrier frequency of the laser pulse, occurring regularly even at far-off resonance frequencies. By analyzing a two-level model, we find that the CEP effect can be attributed to the quantum interference between neighboring multi-photon transition pathways, which is made possible by the broadened spectrum of the ultrashort laser pulse. A general picture is developed along this line to understand the sensitivity of the CEP effect to laser's carrier frequency. Multi-level influence on the CEP effect is also discussed.

physics.atom-ph↗
arXiv2010

The dynamic dipole polarizabilities of the Li atom and the Be+ ion

The dynamic dipole polarizabilities for the Li atom and the Be+ ion in the 2s and 2p states are calculated using the variational method with a Hylleraas basis. The present polarizabilities represent the definitive values in the non-relativistic limit. Corrections due to relativistic effects are also estimated. Analytic representations of the polarizabilities for frequency ranges encompassing the n=3 excitations are presented. The recommended polarizabilities for ^7Li and ^9Be+ were 164.11 \pm 0.03 a.u. and 24.489 \pm 0.004 a.u..

physics.atom-ph↗
arXiv2009

Calculations of polarizabilities and hyperpolarizabilities for the Be$^+$ ion

The polarizabilities and hyperpolarizabilities of the Be$^+$ ion in the $2^2S$ state and the $2^2P$ state are determined. Calculations are performed using two independent methods: i) variationally determined wave functions using Hylleraas basis set expansions and ii) single electron calculations utilizing a frozen-core Hamiltonian. The first few parameters in the long-range interaction potential between a Be$^+$ ion and a H, He, or Li atom, and the leading parameters of the effective potential for the high-$L$ Rydberg states of beryllium were also computed. All the values reported are the results of calculations close to convergence. Comparisons are made with published results where available.

physics.atom-ph↗
arXiv2009

Imaging molecular characterization by high-order above threshold ionization in intense laser field

Using the frequency-domain theory, the high-order above threshold ionization (HATI) of a molecule is treated as a two-step transition: an above threshold ionization (ATI) followed by a laser-assisted collision (LAC). It is found that the HATI spectrum carries three pieces of information: the fingerprint of the molecular wave function lying in the ATI transition, the geometry structure of the molecule lying in the potential scattering between two plane waves, and the interaction between the ionized electron and the laser field lying in a phase factor in the LAC transition, where the phase factor can be regarded as due to the action difference of the classical trajectory before and after the collision within one laser cycle. Based on this picture, it is demonstrated that the skeleton structure of a molecule can be imaged more clearly using a relatively higher frequency laser field due to the simplification of interference originated from the phase factor. This work can shed light on imaging the structure of a complex molecule by a HATI process.

physics.atom-ph↗
arXiv2009

Non-relativistic ab initio calculations for $2^2S$, $2^2P$ and $3^2D$ lithium isotopes: Applications to polarizabilities and dispersion interactions

The electric dipole polarizabilities and hyperpolarizabilities for the lithium isotopes $^6$Li and $^7$Li in the ground state $2^2S$ and the excited states $2^2P$ and $3^2D$, as well as the leading resonance and dispersion long-range coefficients for the Li($2^2S$)--Li($2^2S$) and Li($2^2S$)--Li($2^2P$) systems, are calculated nonrelativistically using variational wave functions in Hylleraas basis sets. Comparisons are made with published results, where available. We find that the value of the second hyperpolarizability of the $2^2S$ state is sensitive to the isotopic mass due to a near cancellation between two terms. For the $3^2D$ state polarizability tensor the calculated components disagree with those measured in the sole experiment and with those calculated semi-empirically.

physics.atom-ph↗
arXiv2009

Laser-assisted collision effect on nonsequential double ionization of helium in a few-cycle laser pulse

Nonsequential double ionization (NSDI) of helium in an intense few-cycle laser pulse is investigated by applying the three-dimensional semi-classical re-scattering method. It is found that the momentum distribution of He$^{2+}$ shows a single-double-single peak structure as the pulse intensity increases. According to the different mechanisms dominating the NSDI process, the laser intensity can be classified into three regimes where the momentum distribution of He$^{2+}$ exhibits different characteristics. In the relatively high intensity regime, an NSDI mechanism named the "laser-assisted collision ionization" is found to be dominating the NSDI process and causing the single peak structure. This result can shed light on the study of non-sequential ionization of a highly charged ion in a relatively intense laser pulse.

physics.atom-ph↗
arXiv1999

Variational calculations on the hydrogen molecular ion

We present high-precision non-relativistic variational calculations of bound vibrational-rotational state energies for the $H_2^+$ and $D_2^+$ molecular ions in each of the lowest electronic states of $Σ_g$, $Σ_u$, and $Π_u$ symmetry. The calculations are carried out including coupling between $Σ$ and $Π$ states but without using the Born-Oppenheimer or any adiabatic approximation. Convergence studies are presented which indicate that the resulting energies for low-lying levels are accurate to about $10^{-13}$. Our procedure accounts naturally for the lambda-doubling of the $Π_u$ state.

physics.atom-ph↗
arXiv1998

Long-range interactions of metastable helium atoms

Polarizabilities, dispersion coefficients, and long-range atom-surface interaction potentials are calculated for the n=2 triplet and singlet states of helium using highly accurate, variationally determined, wave functions.

physics.atom-ph↗
arXiv1996

Long-range interactions of lithium atoms

The long-range interactions of two atoms, of an atom and a dielectric wall, of an atom and a perfectly conducting wall, and of an atom between two perfectly conducting walls are calculated, including the effects of retardation, for Li using dynamic polarizabilities determined from highly correlated, variationally determined wave functions.

physics.atom-ph↗
arXiv1996

Variational calculations of dispersion coefficients for interactions between H, He, and Li atoms

The dispersion coefficients $C_6$, $C_8$, and $C_{10}$ for the interactions between H, He, and Li are calculated using variational wave functions in Hylleraas basis sets with multiple exponential scale factors. With these highly correlated wave functions, significant improvements are made upon previous calculations and our results provide definitive values for these coefficients.

atom-ph↗