The potential energy curves and spectroscopic constants of the ground and 32 low-lying electronic states of ZrC have been studied by employing multireference configuration interaction methods,in conjunction with relativistic effective core potentials and 5s3p3d1f,3s3p1d basis sets con Zr and C,respectively.We have determined that the ground state is 3~(2+).However there are two low-lying ~1SIGMA~+ states(below 5000 cm~(-1))which strongly interact resulting in avoided crossings.The lowest ~1SIGMA~+ state corresponds to a combination of 1 sigma~2 Xsigma~2 1 pi~4 configurations whereas the second is an open shell singlet 1 sigma~2 2sigma~1 3sigma~1 1pi~4.Several avoided crossings were observed,for ~1PI,~3PI,~1DELTA,~3SIGMA~+,and ~3DELTA states.We have identified ~3PI and ~1PI lying at 4367 and 5797 cm~(-1),respectively.The results are in good agreement with the recent experimental findings of Rixon et al[J.Mol.Spectrosc.228,554(2004)],and indicate that the ~3PI-~3SIGMA~+,and ~1PI-~1SIGMA~+,bands located between 16000-19000 cm~(-1)are extremely complex due to near degeneracy of several ~1PI and ~3PI states.We also have identified a ~1SIGMA~+ state in the same region that may interfere with the ~1PI emission bands.The present results not only shed further light into the spectra of ZrC but also predict yet to be observed systems.
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