Theoretical Studies On Laser Cooling Of XH~±(X=B,N,Ga,In) Molecules

In recent years,cold atoms and molecules have attracted much attention from both experimental and theoretical aspects.Many molecular cooling schemes have been reported,and some molecules have been cooled in the laboratory.However,few studies have been reported on molecular ions.Based on the ab initio method,the feasibility of XH^??X=B,N,Ga,In?molecular laser cooling is theoretically analyzed,and the corresponding cooling scheme is designed.The following research has been completed.1.By using the multi-reference configuration interaction method,the potential energy curves and transition dipole moments of the BH⁺and BH^-molecules of ground state 1²?⁺and the low excited state 2²?⁺,1²?and 2²?are calculated using the all-electron basis sets aug-cc-pwCV5Z and aug-cc-PV5Z.Based on the obtained potential energy curve,the vibrational energy levels of four states of BH⁺and BH^-molecules are calculated by solving the Schr?dinger equation of nuclear motion.Then,the spectroscopic parameters are determined from the ro-vibrational levels with Dunham expansion and compared with the theoretical and experimental reports in the literature.In order to construct the laser cooling scheme,we also calculated the transition probability between different vibrational levels of electrons and the spontaneous emission lifetime of the first few vibrational levels in high electronic states.According to the molecular structure and spectral characteristics,the feasibility of laser cooling is analyzed,and the corresponding cooling schemes are designed.2.The structures of NH⁺and NH^-molecules are similar to that of BH⁺and BH^-.We calculated the potential energy curve,the transition dipole moment,the vibrational rotational level and the spectral constant as well as the Frank Condon factor and the radiation life for the 1²?⁺,2²?⁺,1²?and 2²?states of NH⁺cation and NH^-ion.The feasibility of the two molecules laser cooling are confirmed,and the corresponding cooling schemes are given.The results show that the transition probability of NH^-anion is much larger than that of NH⁺cation,but the expected cooling temperature is very low.However,the self-dissociation of NH^-molecules is not easy to form a closed transition cycle.Therefore,it is not easy for NH^-molecules to achieve laser cooling in the experiment.3.Based on atomic-natural orbital?ANO?for Ga,In and H,we obtain the PECs of the ground state 1²?⁺and excited state 1²?.Considering both Ga and In are heavy elements,we show very large relativistic effects and the spin-orbit coupling effects,the PECs and TDMs,ro-vibrational levels,spectroscopic parameters and FCFs of 1²?,1²?_1/2/2 and 1²?_3/2/2 states are obtained.The results show that the?₀₀0 of InH⁺is only 0.68,which can not guarantee t the number of the leaked photons is less,and more laser beams pumping are needed.Therefore,the preparation of InH⁺cation is not easy to achieve in the experiment.According to these characteristics,we have designed the corresponding cooling scheme.