Solid state-like high harmonic generation from cluster molecules with rotational periodicities.

High harmonic generation (HHG) from solid-state crystals in strong laser fields has been understood by the band structure of the solids, which is based on the periodic boundary condition (PBC) due to translational invariance. For the systems with PBC due to rotational invariance, an analogous Bloch theorem can be applied. Considering a ring-type cluster of cyclo[18]carbon as an example, we develop a quasi-band model and predict the solid state-like HHG in this system. Under the irradiation of linearly polarized laser field, cyclo[18]carbon exhibits solid state-like HHG originated from intraband oscillations and interband transitions, which, in turn, is promising to optically detect the symmetry and geometry of molecular or material structures. Our results based on the Liouville-von Neumann equations are well reproduced by the time-dependent density functional theory calculations and are foundational in providing a connection linking the HHG physics of gases and solids.

Ab initio study of spectroscopic properties and anharmonic force fields of MNH2 (M = Li, Na, K).

The spectroscopic properties and anharmonic force fields of NaNH2 are studied in present work by DFT (B3P86 and B3PW91) and MP2 methods in combination with 6-311++G(2d, 2p) and 6-311++G(3df, 2pd) basis sets. The calculated equilibrium geometry, ground state rotational constants and centrifugal distortion constants of NaNH2 at B3P86/6-311++G(3df, 2pd) theoretical level agree very well with the corresponding experimental values. Noteworthy, some spectroscopic constants and anharmonic force fields of NaNH2, which have not been experimentally measured, are firstly predicted. In addition, the spectroscopic properties of KNH2 are also predicted at the B3P86/6-311++G(3df, 2pd) level of theory. The influences of metal atoms on the equilibrium geometry, anharmonic constants, rotational constants, centrifugal distortion constants of MNH2 (M = Li, Na, K) are analyzed intuitively. One can find that the metal atoms affect the rotational constants, part of centrifugal distortion constants (DK, DJK, HK, and HKJ), M-N bond length and some anharmonic constants of MNH2.

Ab initio study of spectroscopic properties at anharmonic force fields of LiNH2.

This work presents a systematic investigation of the spectroscopic properties at anharmonic force fields of ground electronic state ([Formula: see text]) of LiNH2, which are calculated using second-order Møller-Plesset perturbation theory (MP2) and density functional theory (DFT) with hybrid GGA and meta-hybrid GGA (M06-2X) exchange-correlation functional. Two high angular momentum basis sets of 6-311+g (2d, p) and 6-311++g (3df, 2pd) are used. The equilibrium geometries, ground-state rotational constants, harmonic frequencies, and quartic and sextic centrifugal distortion constants of LiNH2 are calculated and compared with corresponding experimental or theoretical data. The predicted accuracy of the calculated constants has been confirmed by analyzing the deviations with respect to experiment. In addition, the anharmonic constants, vibration-rotation interaction constants, force constants, and Coriolis coupling constants of LiNH2 are firstly obtained. The infrared spectrum is predicted and together with the first prediction on the higher-order anharmonic constants contributes to a better understanding of the vibrational and rotational characteristics of LiNH2, thus revealing its internal structure. Graphical abstract The IR spectra and the magnified IR spectra at 3500 cm-1 in harmonic approximations of LiNH2 using B3P86, M06-2X and MP2 methods combining with 6-311++g(3df,2pd).

Ab initio study on the molecular structure and spectroscopic properties of isomers of SO3.

The exploration for the four possible isomers of sulfur trioxide (SO3) has led to the analysis of spectroscopic constants and anharmonic force fields for cis-OSOO, trans-OSOO, OS(=O) O and SOOO. Quantum chemical calculations are performed with Density Functional Theory (DFT) by employing B3LYP, B3P86 and B3PW91 three different functionals, in combination with Dunning's correlation-consistent cc-pVnZ, aug-cc-pVnZ (n = T, Q) basis sets. The equilibrium geometries, energies, force constants, a series of spectroscopic constants of these four isomers of SO3 are calculated. The relationship between their structures and spectroscopic properties are analyzed in detail. The present results well reproduce the previous corresponding theoretical or experimental values. Therefore, we hope that our predictions on the isomers of SO3 can provide the useful reference to further study their spectroscopic properties.