Theoretical Studies On Laser Cooling Of CuH,AuH And SrCl Molecules

Ultra-cold atoms and molecules attracted more and more scholars in related fields to study.They have a wide range of applications in the fields of Bose-Einstein Condensates,precision measurement,cold molecular spectroscopy,Ultra-cold collisions.At present,the study of multi-atom laser cooling scheme has been reported,but the molecular laser cooling research is less.Based on the ab initio theory,we study the CuH,AuH and SrCl molecules by using the Davidson-corrected multi-reference configuration interaction?MRCI+Q?method and quantum dynamics calculation.In order to evaluate the characteristics of ground and low excited states of CuH,AuH and SrCl molecules and the feasibility of laser cooling.We use the atomic-natural-orbital basis sets for Cu,Au,Sr and H atoms and the aug-cc-pV5Z basis set for Cl atoms to calculate ground state and low excitation potential energy curves?PECs?,vibration and rotational properties.Using the MRCI+Q method,the X¹?⁺,A¹?⁺,B¹?⁺,a³?⁺,b³?⁺,e³?⁺,C¹?,D¹?,c³?,and d³?electronic states PECs of the CuH and AuH molecules and the X²?⁺,A²?,B²?,A²?_1/2,and A²?_3/2/2 electronic states PECs of the SrCl molecule were calculated and the transition dipole moment between these electronic states were calculated.Based on the PECs,we calculate the vibrational and rotational energy levels by solving the Schr?dinger equation of nuclear motion.And based on the calculated PECs,the analytical potential energy function?APEF?of CuH,AuH and SrCl molecules is obtained by Morrel-Sorbie?MS?function and least squares method,and the spectral constant of each electronic state of each molecule is calculated according to APEF.The spectroscopic parameters of the CuH,AuH,and SrCl molecules are calculated by fitting the PECs to an analytical function to calculate the higher force constants.The present results of the spectroscopic parameters the CuH,AuH,and SrCl molecules are in agreement with the available experimental values and in the literature,which implies that the present calculations method is credible theoretical level to calculate the electronic properties of the low-lying electronic states of CuH,AuH,and SrCl molecules.The results can be used for the next calculations.By using LEVEL8.2 program,we calculate the Franck-Condon factors?FCFss?for the three molecules for the considered states,and dicuss the feasibility of laser cooling.The optical scheme of the laser cooling for CuH molecule is constructed with A¹?⁺?X¹?⁺as the close-loop transition.Since the FCFs of A¹?⁺?v?=0??X¹?⁺?v?=0?transition is 0.78,it is not enough to provide the number of scattered photons with obvious cooling effect.Therefore,when constructing the laser cooling scheme,it is necessary to increase two in all directions.For the AuH molecule,the optical scheme of the laser cooling is built with D¹??X¹?⁺as the close-loop transition.The FCFs of the D¹??X¹?⁺transition is 0.9862 which means that the AuH molecule meets the necessary requirements for laser cooling.For the SrCl molecule,the FCFss of A²?_1/2,3/2?X²?⁺transitions are 0.942 and 0.946,and he A²?_1/2,3/2?X²?⁺transitions have a shorter lifetime,which is directly used to construct a laser cooling scheme.At the same time,we also determined the wavelengths of the pump lasers used to close the cyclic transitions of CuH,AuH and SrCl molecules.