Dipole and transition moments of SiH, PH and SH by ab initio effective valence shell Hamiltonian method

Excellent Ultracold Molecular Candidates From Group VA Hydrides: Whether Do Nearby Electronic States Interfere?

By means of highly accurate ab initio calculations, we identify two excellent ultracold molecular candidates from group VA hydrides. We find that NH and PH are suitable for the production of ultracold molecules, and the feasibility and advantage of two laser cooling schemes are demonstrated, which involve different spin-orbit states (A 3 Π 2 andX 3 Σ 1 - ). The internally contracted multireference configuration interaction method is applied in calculations of the six low-lying Λ-S states of NH and PH with the spin-orbit coupling effects included, and excellent agreement is achieved between the computed and experimental spectroscopic data. We find that the locations of crossing point between theA 3 Π andΣ - 5 states of NH and PH are higher than the corresponding v' = 2 vibrational levels of theA 3 Π state indicating that the crossings with higher electronic states would not affect laser cooling. Meanwhile, the extremely small vibrational branching loss ratios of theA 3 Π 2 →a 1 Δ 2 transition for NH and PH (NH: 1.81 × 10-8; PH: 1.08 × 10-6) indicate that thea 1 Δ 2 intermediate electronic state will not interfere with the laser cooling. Consequently, we construct feasible laser-cooling schemes for NH and PH using three lasers based on theA 3 Π 2 →X 3 Σ 1 - transition, which feature highly diagonal vibrational branching ratioR 00 (NH: 0.9952; PH: 0.9977), the large number of scattered photons (NH: 1.04×105; PH: 8.32×106) and very short radiative lifetimes (NH: 474 ns; PH: 526 ns). Our work suggests that feasible laser-cooling schemes could be established for a molecular system with extra electronic states close to those chosen for laser-cooling.

Theoretical study of the insertion reaction of singlet phosphinidene with hydrogen sulfide

The mechanism of the insertion reaction of singlet phosphinidene with hydrogen sulfide has been studied at HF/6-31G(d), MP2(full)/6-31G(d) and CCSD(T)/6-311 + G(d, p) levels, taking place through a three-membered ring transition state. The thermodynamic and kinetic properties of this reaction channel in the temperature range of 100–1500K have been studied, and it is concluded that the reaction is thermodynamically favoured at low temperature and kinetically favoured at high temperature.

Accurate Frequency Determination of Vibration-Rotation and Rotational Transitions of SiH. THE ASTROPHYSICAL JOURNAL 2017;849:60. [PMID: 29142330 PMCID: PMC5683345 DOI: 10.3847/1538-4357/aa8fca]

The fundamental 28SiH+ ion has been characterized in a collaborative work, utilizing a hollow-cathode-discharge laser-spectrometer and a cryogenic ion trap spectrometer. Twenty-three vibration-rotation transitions around 4.75 μm have been detected with high accuracy. This has facilitated the first direct measurement of the pure rotational transition J = 1 ← 0 at 453056.3632(4) MHz in the trap spectrometer. The measured and accurately predicted transitions enable the search for this ion in space with IR and sub-mm telescopes.

A theoretical study on low-lying electronic states and spectroscopic properties of PH

The low-lying electronic states (X(3)∑(-), a(1)Δ, b(1)Σ(+), A(3)Π, c(1)Π and (5)∑(-)) of the PH species correlating with the first three dissociation channels have been investigated at the MRCI+Q/aug-cc-PV5Z level of theory. Accurate adiabatic potential energy curves and spectroscopic constants (T(e), R(e), ω(e)χ(e), ω(e), B(e), D(e)) of these electronic states have been reported. Effect of the spin-orbit coupling on the A(3)Π and (5)∑(-) states of the PH has been calculated, which lead to the spin-orbit-induced predissociation of the A(3)Π state. Electronic transition moment, Einstein coefficients and Franck-Condon factors for the A(3)Π - X(3)∑(-) system have been calculated. Dipole moment functions (μ(e)) and radiative lifetime (τ(v')) for the A(3)Π state has also been determined. The radiative lifetime for A(3)Π - X(3)∑(-) transition is computed and compared with the available data.

Fourier Transform Emission Spectroscopy of the A2Delta-X2Pi Transition of SiH and SiD

The emission spectra of the A2Delta-X2Pi transition of SiH and SiD have been observed at high resolution using a Fourier transform spectrometer. The molecules were excited in a Si hollow cathode lamp by passing a discharge through a mixture of Ne and a trace of H2 or D2. The present data, combined with the previous infrared vibration-rotation measurements, have been used to determine improved molecular constants for the ground and excited states of SiH and SiD. Copyright 1998 Academic Press.

Calculation of static molecular properties in the framework of the unitary group based coupled cluster approach

The recently developed and implemented state selective, fully spin-adapted coupled cluster (CC) method that employs a single, yet effectively multiconfigurational, spin-free reference and the formalism of the unitary group approach (UGA) to the many-electron correlation problem, has been employed to calculate static electric properties of various open-shell (OS) systems using the finite field (FF) technique. Starting with the lithium atom, the method was applied at the first-order interacting space single and double excitation level (CCSD(is)) to several first- and second-row hydrides having OS ground state, namely to the CH, NH, OH, SiH, PH, and SH radicals. In the case of NH we also considered three OS excited states. In all cases the dipole moment and polarizability were determined using a high quality basis set and compared with the experiment, whenever available, as well as with various configuration interaction results and other theoretical results that are available from the literature. The agreement of our CCSD(is) values with experiment is very satisfactory except for the 3Σ− ground state of the NH radical, where the experimentally determined dipole moment is too small. No experimental data are available for the corresponding polarizabilities. It is also shown that the FF technique is not suitable for calculations of higher order static properties, such as the hyperpolarizability β and γ tensors. For this reason we formulate the linear response version of our UGA-based CCSD approach and discuss the aspects of its future implementation. Key words: static molecular properties, dipole moments, polarizabilities, free radicals, unitary group based coupled cluster method, linear response theory, finite field technique.