物理学报2017，Vol.66Issue(10)：61-67,7.DOI:10.7498/aps.66.103101
O2分子B3∑u-态势能曲线的从头计算
Ab initio calculation of the potential curve of B3∑u-state of O2
摘要
Abstract
The B3∑u-state of O2 molecule is an upper state of the most strongly allowed triplet-triplet (B3∑~ ← X3∑g-)absorption,the Schumann-Runge (SR) transition,which plays a crucial role in protecting the earth from suffering UV radiation.Photo-dissociation of O2 molecule in the SR transition is the major source of odd oxygen (O and O3) in the stratosphere.Comprehensive knowledge of the electronic states,especially their potential energy curves (PECs),is necessary to understand those phenomena.In this paper,we calculate the PEC of Ba∑~ state of O2 by using the internally contracted multi-reference configuration interaction including Davison correction method,which is denoted by icMRCI+Q,and utilize the complete active space self-consistent field (CASSCF) function as a reference function.The calculation is implemented in the MOLPRO suite of codes.Firstly,we carry out the state-averaged (SA) calculation on the four lowest states,A'3Au,B3∑u-,23Au and 23∑u-states,which are in the same irreducible representation of symmetric group.The active space of CASSCF consists of full valence space.The augmented correlation-consistent aug-cc-pV5Z basis set is used.The results show that the PEC of B3∑u-state does not displays double well structure,which is contradictory to Liu's result (Spectrochimica Acta Part A:Molecular and Biomolecular Spectroscopy 2014 124 216).By analyzing the PEC structure,we find that the double well of Liu's result comes from the "root flipping",that is,the PEC interchange from B3∑u-state into 23Au state.In our case the "root flipping" is avoided by the SA calculation.Secondly,in order to ensure that the most important configurations are included in the reference function,we calculate the PEC of BaEu-state of O2 molecule at CASSCF/aug-cc-pVTZ level by changing the active space.We find that the bound well of the PEC will not appear unless the active space includes 2πu orbital which is beyond the full valence space.That means that the Rydberg configurations including 2πu orbital play a crucial role in forming the bound well.And the result is further improved by adding into the active space another two orbitals 4σg and 4σu whose orbital energies are both less than 2π,u.Finally,we add the Rydberg configurations into the multi-reference configuration function by putting 2πu,4σg,4σu into the active space and then carry out the calculation at an icMRCI+Q/aug-cc-pVTZ level.The obtained B3∑u-state PEC and its spectroscopic constants are in good agreement with the experimental data compared with previous results.Moreover,the process we determine the reference configurations is useful for making accurate calculation at an MRCI level on other species.关键词
O2分子的B3∑u-态/多参考组态相互作用/势能曲线/光谱常数Key words
B3∑u-state of O2/internally contracted multi-reference configuration interaction/potential energy curve/spectroscopic constants引用本文复制引用
李晨曦,郭迎春,王兵兵..O2分子B3∑u-态势能曲线的从头计算[J].物理学报,2017,66(10):61-67,7.基金项目
国家自然科学基金(批准号:11474348,61275128)资助的课题.Project supported by the National Natural Science Foundation of China (Grant Nos.11474348,61275128). （批准号:11474348,61275128）
