A Combined Ab Initio/Franck-Condon Study of the A-X Single-Vibronic-Level Emission Spectrum of CCI_2 and the Photodetachment Spectrum of CCI_2

摘要

State-of-the-art ab initio calculations have been carried out on the X~1A_1,a~3B_1,and A~1B_1 states of CCl_2 and the X~2B_1 state of CCI_2~-.Franck-Condon factors including anharmonicity have been calculated,between the CO_2 states,and between the CCl_2~- X~2B_1 state and the CCI_2 states.They are used to simulate the A-X single-vibronic-level (SVL) emission spectra of CCl_2 determined by M.-L Lui et al.[PCCP 2003,5,352] and the 364 nm laser photo-detachment spectrum of CCl_2~- obtained by R.L Schwartz et al.[J.Phys.Chem.A 1999,103,8213].Comparison between simulated and observed spectra confirms the vibrational assignments of the X~2B_1 SVL emission spectra and the T_0 position of the A~1B_1 state of CCl_2.For the photodetachment spectrum of CCl_2~-,spectral simulation shows that the higher binding energy a~3B_1 (CCI_2)<-X~2B_1(CCI_2~-) band is well separated from the X~1A-1,(CCI_2)<-X~2B_1(CCI_2~-) band.It is concluded that the observed second band,which overlaps heavily with the X_1A_1,(CCI_2)<-X~2B_1 (CCI_2~-) band in the photodetachment spectrum of CCl_2~- cannot be assigned to the CO_2(a~3B_1) + e->CCl_2~-(X~2B_1) detachment process.Further ab initio calculations carried out in the present investigation support the suggestion that the second band in the 364 nm photodetachment spectrum of CCl_2 is due to detachment from an excited state of CCl_2 ,a linear quartet state,to a triplet state of CCl_2.These calculations identify the anionic state to be the lowest ~4SIGMA_g~- (~4sigma~-) state,which photodetaches vertically to the ~3SIGMA_g~- (~3SIGMA~-;adiabatically a~3B_1) and/or ~3II_U (~3II) states of CCI_2 to give the second band observed in the 364 nm photodetachment spectrum of COl_2~-.