Theoretical Study On The Electronic Structure And Spectroscopy Of The Alkali-Alkaline Earth Metal Molecules With The MRCI-F12 Method

Due to ultracold molecules play an important role in various fields,the investigation on the Alkali（AK）-Alkaline Earth（AKE）metals molecules therefore attract more attention.In this work,using the explicit correlation multi-reference configuration interaction method（MRCI-F12）,we have studied the electronic structure and spectrum of the AK-AKE metals molecules and aluminium oxide cation.The main contents are as following:1.The 7 states of LiX、NaX（X=Be、Mg）which correspond Li/Na（²S_g）+X（¹S_g）、Li/Na（²P_u）+X（¹S_g）and Li/Na（²S_g）+X（³P_u）and the 24 states of AlO⁺cation which correspond Al⁺（¹S_g）+O（³P_g）、Al⁺（¹S_g）+O（¹D_g）、Al⁺（¹S_g）+O（¹S_g）and Al⁺（³P_u）+O（³P_g）have been studied with MRCI-F12 method,and then depicted the PECs based on the calculations.As shown in PECs,we found that the ground state X²Σ⁺of LiX、NaX（X=Be、Mg）is the only state that corresponds the first dissociation limit Li/Na（²S_g）+X（¹S_g）（X=Be、Mg）,and the first A²Πand second B²Σ⁺excited states correspond the second dissociation limit Li/Na（²P_u）+X（¹S_g）（X=Be、Mg）.Also,solving the radial Schr?dinger equation can determine spectrum constants which fairly correspond with the existed experimental and theoretical data.Plus,the same valence electrons occupied allows the LiX、NaX（X=Be、Mg）molecules have the similar PECs shape.The electrons occupy in different bonding or antibonding orbital makes the first excited A²Πstate has deeper dissociation energy than that of the ground X²Σ⁺state.Take the Li Be molecule as an example,the dissociation energy respectively for X²Σ⁺and A²Πis 0.3161 and 1.6117 eV.Furthermore,with the increasing of the contained electrons,the dissociation energy becomes smaller,the results are 0.3161,0.1639,0.1245 and 0.073 eV,respectively.Turning to the AlO⁺cation,in order for determining the ground state and studying the predissociation mechanisms of the X¹Σ⁺,A¹Π,and 2¹Σ⁺states,the PECs were calculated and the spectroscopic constants were determined.Moreover,we also study the high-excited states of AlO⁺cation,especially on the two-potential-well feature of 2¹Σ⁺state.2.Also,the permanent dipole moments（PDMs）of LiX、NaX（X=Be、Mg）and AlO⁺cation have been calculated based on the MRCI wavefunction.We find out from the figure is with the increasing of the internuclear distance R of LiX、NaX（X=Be、Mg）molecule,the calculated PDMs tend to zero,which confirms that the dissociation limit consist of neutral atom.However,we found that the permanent dipole moments of AlO⁺cation tend to the negative value,which confirms that the dissociation limit consist of cation.3.In this work,We also study the interaction between the states by the calculated spin-orbit matrix elements,predicting the predissociation of the AlO⁺cation,mainly including the predissociation of X¹Σ⁺,A¹Π,and 2¹Σ⁺by the b³Σ^-channel.4.Finally,the Franck-Condon factors were obtained with the LEVEL,plus the transition dipole moments value,we can calculate the radicative lifetime of the excited states.Based on the f₀₀=0.99525 and v（0-0）=84.2 ns of the B¹Σ⁺state,we predicted the LiBe molecule can be a candidate molecule of the cooling molecule.