A Theoretical Study on Laser Cooling Feasibility of Group IVA Hydrides XH (X = Si, Ge, Sn, and Pb): The Role of Electronic State Crossing

Abstract

The feasibility of direct laser cooling of SiH, GeH, SnH, and PbH is investigated and assessed based upon first principles. The internally contracted multi-reference configuration interaction method with the Davidson correction is applied. Very good agreement is obtained between our computed spectroscopic constants and the available experimental data. We find that the locations of crossing point between the B 2 − and A 2 states have the tendency of moving downwards from CH to SnH relative to the bottom of the corresponding A 2 potential, which precludes the laser cooling of GeH, SnH, and PbH. By including the spin-orbit coupling effects and on the basis of the A 2 5/2 →X 2 3/2 transition, we propose a feasible laser cooling scheme for SiH using three lasers with wavelengths varying from 400 to 500 nm, which features a very large vibrational branching ratio (0.9954) and a very short radiative lifetime (575 ns). Moreover, similar studies are extended to carbon monosulfide (CS) with a feasible laser cooling scheme proposed. The importance of electronic state crossing in molecular laser cooling is underscored, and our work suggests useful caveats to the choice of promising candidates for producing ultracold molecules.

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

“…The extremely small vibrational branching loss ratios of the → transition for NH and PH indicate that the intermediate electronic state will not interfere with the laser-cooling. Hence, we will construct feasible three-laser cooling schemes for NH and PH on the basis of the → transition in the next section, which satisfy all known criteria including the fourth one proposed in our recent work ( Li et al, 2020 ).…”

“…It is known ( Fu et al, 2016 ; Yuan et al, 2019 ; Li et al, 2021 ) that, a suitable candidate for laser cooling needs to satisfy three criteria: highly diagonal Franck-Condon factors (FCFs), an extremely short radiative lifetime, and no interference from the intermediate electronic states. In our recent work, the fourth criterion for molecular laser cooling was proposed, that is, no electronic-state crossing, or the crossing point between the two states was high enough in energy ( Li et al, 2020 ). Consequently, all electronic states close to those chosen for laser-cooling should be calculated and checked beforehand in selecting laser-cooling candidates.…”

Progress in Mesoporous Silica Nanoparticles as Drug Delivery Agents for Cancer Treatment

“…For cancer treatment, there is a specific enzyme present in this tumor microenvironment. Therefore, by employing a carrier with a component that sensitive to the present enzyme, a control released system through enzymatic cleavage is obtained [ 199 ]. Cai et al reported on the production of enzyme responsive MSNs with chitosan as the gate responsible for trapping the drug in the MSNs pores.…”

A theoretical study on laser cooling feasibility of XH (X = As, Sb and Bi): effects of intersystem crossings and spin–orbit couplings

“…11,12 Recently, Bian proposed the fourth criterion that there should be no electronic-state crossing, or the crossing point is high enough in energy relative to the ground vibrational levels. 13 In this previous work, 13 the crossings considered are between two electronic states of the same spin multiplicity. Here, we extend the fourth criterion to the case involving the crossings between electronic-states of different spin multiplicities, where spinorbit couplings (SOCs) need to be evaluated.…”