Observation of dipole forbidden transitions of C2

通过可见光波段系统观察到C2的较高振动能级。根据D-C带系的室温光谱，精确地测定了C2的C态分子常数。我们发现，c(v=1)态与a(v=7)态存在能级交叉。对c(v=1)和a(v=7)态进行了微扰分析。由实验测得的精确振子能级表明，单态A(v=2)与三态a(v=7)位置非常接近，相互作用。然而，观察到的A(v=2)态能级移动的方向不能用单三重态能隙的文献值T0(a-X)=610.4 cm-1来解释。结果表明，单重态-三重态能隙应从文献值修正3 cm-1以上。

Higher vibrational levels of C2 were observed through visible band systems. Molecular constants of the c-state of C2 were precisely determined from room-temperature spectra of the d-c band system. We found that the c(v=1) state shows a level-crossing with the a(v=7) state. The perturbation analysis between the c(v=1) and a(v=7) states has been carried out. Accurate rovibronic level energies which have been determined from the experiment indicate that the singlet A(v=2) state is located very close to the triplet a(v=7) state, interacting with each other. However, the direction of the observed level shifts in the A(v=2) state cannot be explained with the literature value of the single-triplet energy gap, T0(a-X)=610.4 cm-1. It is concluded that the singlet-triplet energy gap should be modified by more than 3 cm-1 from the literature value.