Theoretical Investigations On The Spectroscopic Properties For Some Low-lying Electronic States Of SiP And AlS Radical

The potential energy function of diatomic molecules has always been an important and basic theoretical problem in the study of atomic and molecular physics,and it is also the basis of many experimental studies and theoretical calculations.The molecular potential energy curves,spectral constants,transition properties and radiative lifetimes of the low electron states of silicon phosphide and Aluminum sulfide have been studied.First,The potential energy curves of the X~2?,A~2?⁺,B~2?,C~2?⁺,a~4?,b~4?⁺,c~4?,and d~4?^–states of Si P molecule and the transition dipole moments of the transitions between these states were calculated using the CASSCF method,followed by the ic MRCI approach.The radiative lifetimes were about 0.1–10and 1–10000 ms for the A~2?⁺and b~4?⁺states,respectively.The lifetimes were approximately 100,10–100,10,and 0.1–1?s for the B~2?,c~4?,d~4?^–,and C~2?⁺states,respectively.The spin–orbit coupling constants of the X~2?,B~2?,a~4?,and b~4?⁺states were determined.Including the spin–orbit coupling effect,the radiative lifetimes of the A~2?⁺_1/2,B~2?_1/2,B~2?_3/2,C~2?⁺_1/2,a~4?-_1/2,a~4?_1/2,a~4?_3/2,a~4?_5/2,b~4?⁺_1/2,and b~4?⁺_3/2 states were calculated.The radiative lifetimes were approximately 0.1,0.1,0.1–1,and 10 s for the a~4?-_1/2,a~4?_1/2,a~4?_3/2,and a~4?_5/2states,respectively.Among the spontaneous emissions between these?states,those from the C~2?⁺_1/2 state to the X~2?_3/2,X~2?_1/2,and A~2?⁺_1/2 states were the strongest.The results calculated herein indicated that the strong spontaneous emissions originated from the lower vibrational states of the C~2?⁺_1/2 state.Furthermore,almost all the strong emissions were distributed in the visible region.Therefore,these strong emissions might be detected in outer space.The radiative–lifetime distribution of each level?versus the rotational quantum number J was evaluated for??15 and J?69.5 of several?states.Secondly,use the ic MRCI method to calculate the potential energy curves of X~2?⁺,A'~2?,A~2?⁺,1~2?,1~2?^-,and B~2?of an aluminum sulfide radical and the transition dipole moments between them.core–valence correlation and scalar relativistic corrections and spin-orbit coupling effects are taken into account.The radiative lifetimes of the 1~2?and 1~2?^-states are approximately 10~3–10~2 and 10~2–10 us.For the A~2?⁺,and B~2?states,their radiative lifetimes are about 10~3–10~2 and 10~2 ns,respectively.Among the spontaneous transitions generated in the?state,A'~2?_3/2?X~2?+_1/2 and A'~2?_1/2?X~2?+_1/2 are strong transitions.These strong transitions from the A'~2?^<sub><sub>3/2X~2?⁺_1/2 and A'~2?^<sub><sub>1/2X~2?⁺_1/2 systems are located in the infrared and visible light regions;these strong transitions,especially those in the infrared region,are strong enough,They can penetrate the atmosphere to reach the earth;therefore,it is possible to detect them from ground observations.The transition intensity and spectral range of spontaneous emission between ground state and low excited state were determined by the study of silicon phosphide and aluminum sulfide radicals.The transition properties reported in this study are expected to provide useful guidance for searching for these two radicals in outer space.