MRCI Study of the Electronic Structure and Transition Properties of a Tin Dimer.

The ground and excited states of Sn2 are calculated using the multireference configuration interaction method combined with Davidson correction (MRCI+Q). The influence of the spin-orbit coupling (SOC) effect on the electronic structure is also considered by the state interaction method of Breit-Pauli Hamiltonian. In the calculations, the potential energy curves and spectroscopic constants of 23 Λ-S states and 31 Ω states of Sn2 are obtained. The prominent spectral features in the visible region, new constants, and potential energy curves are discussed. The intensity of weak magnetic and quadrupole transitions in the near IR spectra is also calculated. From a computational point of view, we predict that the weak v'(0-2)-v″(0-5) bands of the magnetic b1Σg,0++-X3Σg,1(Ms=±1)- transition may be detected experimentally; the sub-bands (0, 0), (1, 0), and (2, 0) of the a1Δg,2-X3Σg,1(Ms=±1)- transition also may be observed in experiments since they are not overlapped by the strong electric dipole transition in the same IR region. According to the SOC matrix elements and contributions of the 15Πu0+, 15Πu1 (|Σ| = 0), and 15Πu1 (|Σ| = 2) states to the predissociation line width of the 13Σu- -X3Σg1- transition, the broading and other predissociation features of the 13Σu- state are analyzed. From our calculations, it follows that the strong coupling between the bound 13Σu- state and the repulsive 15Πu state causes the predissociation of the 13Σu- state at the vibrational levels v' ≥ 8. In addition, our results suggest that the previously observed bands of Sn2 in the visible range of 19000-20000 cm-1 should be reassigned into the mixing transitions among the X3Σg,1--23Σu,0-+ and X3Σg,0+--23Σu,1+ manifold. The results are expected to provide new comprehensive information for better understanding the spectra and dynamics of the electronic excited states of the Sn2 molecule.

Ab initio study on the singlet states of Zn-RG (RG = He, Ne, Ar, Kr, Xe, Rn) molecules.

The computations on the potential energy curves (PECs) oftheground state and low-lying singlet excited states for Zn-RG (RG = He, Ne, Ar, Kr, Xe, Rn) molecule have been carried out using coupled-cluster with single and double excitations (CCSD), coupled-cluster with single and double excitations and perturbative contribution of connected triple excitations (CCSD(T)) methods and the equation-of-motion coupled cluster method restricted to single and double excitations (EOM-CCSD). The spectroscopic constants of all the bound states of Zn-RG have been calculated, and comparisons with the available experimental and theoretical works have been made for the ground state and C1Π state of the Zn-RG complexes, reasonable agreement is found. The transition dipole moments (TDMs) functions of C1Π-X1Σ+ and D1Σ+-X1Σ+ transitions, the vibrational band origins, rotational constants and Franck-Condon factors of C1Π-X1Σ+ transition have also been reported, which would be of value to understand the transition properties of Zn-RG. Our study is expected to be helpful for deep understanding on the electronic structure and spectroscopy of Zn-RG van der Waals molecules.

Spectroscopic properties and spin-orbit coupling of electronic excited states of the germanium dimer.

The electronic structure and spectroscopic properties of the germanium dimer have been investigated by high-level ab initio calculations with consideration of spin-orbit coupling (SOC). The potential energy curves (PECs) of 19 Λ-S states, as well as those of 52 Ω states generated from the Λ-S states, are calculated by the multireference configuration interaction plus Davidson correction (MRCI + Q) method. The properties of the F3Σ+u1-X3Σ-g1 and H3Σ-u1-X3Σ-g1 transitions as well as the interactions of the F3Σ+u and H3Σ-u states with other excited states induced by SOC are investigated based on the calculated SO matrix and the PECs of the Ω states. Our results indicate that the previously observed spectra of Ge2 in the range 20 500-22 000 cm-1 should be assigned as the transition between the Ω = 1g component of the X3Σ-g state and Ω = 1u of the F3Σ+u state. Moreover, owing to the strong SOC with the repulsive 25Πu state, the H3Σ-u state is predissociative, leading to the Ge(3P2) + Ge(3P1) channel at vibrational levels higher than v' = 6. Our theoretical study would provide comprehensive information and shed light on understanding the spectroscopy and dynamics of the electronic excited states of Ge2.

Theoretical study on predissociation of B3Σu- of sulfur dimer.

A high level ab initio study on electronic states of sulfur dimer S2 is carried out by utilizing multi-reference configuration interaction plus Davidson correction (MRCI+Q) method. The modification to the electronic structures caused by spin-orbit coupling (SOC) effect is taken into consideration by the state-interacting method with the full Breit-Pauli Hamiltonian. The potential energy curves (PECs) of 19 Λ-S states and 52 Ω states generated from the Λ-S states are calculated. With the aid of calculated SOC matrix elements and the PECs of the Ω states, we discuss the predissociaiton of the B3Σu- state. The variation of line width of B3Σu-- X3Σg- transitions with vibrational quantum number v' of the B3Σu- are determined from Fermi golden rule calculations. Our study indicate that the predissociation of the B3Σu- state is induced by the strong spin-orbit coupling with different electronic excited states, resulting in the abnormal dependence of the dissociation rate on vibrational states.

Laser-cooling with an intermediate electronic state: Theoretical prediction on bismuth hydride.

The possibility of laser cooling of bismuth hydride (BiH) molecules has been investigated based on high-level ab initio calculations by considering the core-valence and the spin-orbit coupling (SOC) effects. The potential energy curves of the 12 Λ-S states as well as the 25 Ω states that split from them via SOC are obtained by multireference configuration interaction plus the Davidson correction. The properties of b-X transition are investigated. Based on our calculations, we show that the transition between Ω states b0+-X10+ of BiH is a possible candidate for laser cooling, with consideration of the intermediate Ω state X21. An optical cycling scheme is proposed by utilizing four lasers at wavelengths around 471 and 601 nm with 5400 cycles for photon absorption/emission and a sub-microkelvin temperature. Our study should shed some light on searching for possible molecular candidates for laser cooling with the existence of an intermediate electronic state.

Constructing Uniform Core-Shell PPy@PANI Composites with Tunable Shell Thickness toward Enhancement in Microwave Absorption.

Highly uniform core-shell composites, polypyrrole@polyaniline (PPy@PANI), have been successfully constructed by directing the polymerization of aniline on the surface of PPy microspheres. The thickness of PANI shells, from 30 to 120 nm, can be well controlled by modulating the weight ratio of aniline and PPy microspheres. PPy microspheres with abundant carbonyl groups have very strong affinity to the conjugated chains of PANI, which is responsible for the spontaneous formation of uniform core-shell microstructures. However, the strong affinity between PPy microspheres and PANI shells does not promote the diffusion or reassembly of two kinds of conjugated chains. Coating PPy microspheres with PANI shells increases the complex permittivity and creates the mechanism of interfacial polarization, where the latter plays an important role in increasing the dielectric loss of PPy@PANI composites. With a proper thickness of PANI shells, the moderate dielectric loss will produce well matched characteristic impedance, so that the microwave absorption properties of these composites can be greatly enhanced. Although PPy@PANI composites herein consume the incident electromagnetic wave by absolute dielectric loss, their performances are still superior or comparable to most PANI-based composites ever reported, indicating that they can be taken as a new kind of promising lightweight microwave absorbers. More importantly, microwave absorption of PPy@PANI composites can be simply modulated not only by the thickness of the absorbers, but also the shell thickness to satisfy the applications in different frequency bands.