• Abstract

• Abstract

Time dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate excited state intramolecular proton transfer (ESIPT) properties of 2-hydroxypyrene-1-carbaldehyde (HC). Our calculated results of the primary bond lengths and infrared vibrational spectroscopic information show that, upon photoexcitation, the intramolecular hydrogen bond is significantly strengthened in S_1 state,which facilitates the proton transfer process effectively. Furthermore, the electron density distributions of frontier molecular orbitals were demonstrated to be a positive factor for the ESIPT. By the monitor of the characteristic peaks stretching vibration of O-H group in the IR spectra, we have further confirmed the occurrence of ESIPT. The constructed potential energy surface of the S_1 state has also been used to explain the proton transfer process and evaluate the radiationless pathway, indicating that the ESIPT process occurs most easily in HC molecule.

• Abstract

High-level ab initio calculations utilizing explicitly correlatedmulti-reference configuration interaction method (MRCI-F12), considering Davidson modification(Q), core-valence correlation correction(CV) and scalar relativistic correction(SR),were performed to compute the Born-Oppenheimer potential energy curve (PEC) of the ground state X¹Σ^+ of NaH. On the base of the PEC, we obtained vibrational and rotational energy levels information of the ground state X¹Σ^+. The vibrational and rotational spectroscopic constants of X¹Σ^+ were compared with the available experimental values. We also report rotation-vibration spectra of the ground state for the isotopes of NaH, NaD and NaTmolecules. The equilibrium internuclear distances R_e and dissociation energies D_e were calculated to be 1.8865 Å and 15823.29cm^{-1} for the ground state X¹Σ^+ of NaH, which are in good agreement with the experimental results of 1.8859 Å and 15815 ± 5cm^{-1}.

• Abstract

By solving the time-dependent Schrödinger equation (TDSE) accurately with time-dependent generalized pseudospectral (TDGPS) method, we theoretically investigated the high-order-harmonic generation (HHG) from three dimensional (3D) Hydrogen atom in ultraviolet (UV)-assisted chirped fields. When a 128 nm UV pulse is added on a chirped fundamental field, the HHG spectra is greatly broadened and enhanced, which is quite similar as the HHG from H atom initially prepared in the first excited state in the chirped field only. Besides, the HHG of H atom in the combination of a chirped fundamental field and a 256 nm UV pulse case is also investigated. The HHG process is illustrated by the semi-classical three-step model and the time-frequency analysis. The ionization probability and electron wavepacket as functions of time are also calculated to further illustrate this phenomenon. Furthermore, we also discuss the influence of time delay between the chirped fundamental field and the 128 nm UV pulse on HHG process. Finally, by superposing the harmonics in the range of 200th-260th order, an isolated attosecond pulse with a duration of about 64 as can be generated.

• Abstract

We theoretically study the high-order harmonic and the isolated attosecond pulse generation in the near-infrared (IR) (3-fs, 800 nm) laser pulse by adding a terahertz (THz) controlling field with proper phases. It is found that the high-order harmonic spectrum in the IR pulse by adding a terahertz field is broader and smoother than that in the single IR pulse. The underlying physical mechanism is illustrated by means of the time-frequency analysis and the three-step model. We calculate the ionization rate by ADK model to further demonstrate the process of high-order harmonic generation. By superposing a proper range of harmonic spectrum, an isolated attosecond pulse with the duration of 71 as is obtained.