Spectral Calculations Of Hydride Diatomic Molecules And Its Application In Laser Cooling

Hydrogen is one of the earliest elements discovered and related to human beings.It is widely distributed in the universe and the natural world.Hydride molecules contain many important organic and inorganic molecules?such as H₂O,CH₄,C₂H₅OH,etc.?and are closely related to our lives.The hydride diatomic molecules,as the simplest hydride molecules,have attracted the attention of researchers.Spectroscopy is known as the“fingerprint”of matter,and it is the most direct reflection of the internal structure and characteristics of atomic molecules.Therefore,it has always been a hot topic to study the energy level distribution and spectral characteristics of atomic and molecular,either by spectral experiment or theoretical calculations.In addition,hydride diatomic molecules have an unique advantage in the study of laser cooling:the Franck-Condon?F-C?factor with highly diagonalized distribution;shorter spontaneous emission lifetime.In this work,five low-lying potential energy curves?PECs?and transition dipole moments?TDM?X²?⁺,A²?,B²?⁺,a⁴?and b⁴?⁺of BX⁺?X=H,D,T?are calculated based on consistent basis set aug-cc-PV5Z by using internally contracted multi-reference configuration interaction?MRCI?approach.In order to improve the reliability of data,Davidson modification and scalar relativistic correction are considered in the calculation.In addition,the spin-orbit coupling effect of A²?state is considered.According to the calculation results,ro-vibrational levels of theses electronic states are derived through solving the radial Schr?dinger equation,and then the molecular parameters,F-C factors and radiation life are obtained by fitting and calculations.The F-C Factors(BH⁺:f₀₀=0.945,BD⁺:f₀₀=0.925 and BT⁺:f₀₀=0.913)for A²?47?_1/2??'=0?-X²?50?⁺??"=0?,and the radiative lifetimes?BH⁺:?=239 ns,BD⁺:?=236 ns and BT⁺:?=235 ns?for the A²?47?_1/2??'=0?.In addition,based on the pseudopotential basis set ecp28mdf is used for Ag atom and aug-cc-pVTZ for ^1,2H atom,the PECs of X¹?50?⁺,A¹?50?⁺,C¹?,a³?,a'³?50?⁺,b'³?50?⁺states and the TDM of X¹?50?⁺-A¹?50?⁺for Ag^1,2H is calculated at the level of MRCI theory.This calculation is based on the Douglas-Kroll theory of relativity and considers the influence of the inner connected electrons.Then,the F-C factors and the radiation lifetime?of A¹?50?-X¹?50?⁺were calculated by LEVEL8.0 procedure.The results:AgH(f₀₀=0.994,?=22.3 ns);AgD(f₀₀=0.995,?=22.2 ns).The data show that both AgH and AgD molecules have highly diagonal distribution FCFs,and?is very short.Therefore,an optical-cycle for Doppler laser cooling scheme has been proposed:A²?47?_1/2???=0?-X²?50?⁺???=0,1?,where the??=0 contains 2 rotational level,??=0 and??=1 contains 6and 4 rotational level,respectively.According to the scheme,we simulate the dynamic process of the molecular population in laser cooling.For the AgH molecule,main beams with wavelength?=338.4 nm and repumping lasers?'=357.9 nm to drive the transition of|X¹?50?⁺,?"=0 1>-|A¹?50?⁺,?'=0>.For the AgD molecule,the wavelength of the four-beam laser is?=338.6 nm and?'=352.4 nm.The results show that the BH⁺series molecules need to scatter8450 photons from 300 K to 5 mK temperature,which takes 41 ms and the cooling efficiency is 92%.AgH and AgD can be reduced from 25 mK to 2 mK at a distance of 78 and 67 cm,and the cooling time is 14.7 and 13.1 ms,respectively.