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Theoretical study on the ground and excited states of dicyanocarbene (C3N2) and its isomers: a low-temperature matrix emission spectrum attributable to 3-cyano-2H-azirenylidene.

Ab initio calculations are used to characterize the ground and low lying excited electronic states of selected dicyanocarbene (C(3)N(2) or C(CN)2) isomers. Our calculated ground state geometries and the corresponding vibrational frequencies agree well with available experimental and theoretical data, thereby providing the reliability of the predicted quantities. The present calculations are used to identify the possible emitting species for some unidentified emission bands observed in certain low-temperature matrices. It is found that the 1(3)A' --> X(1)A' transition of 3-cyano-2H-azirenylidene, that is, cyclic C(2)N-CN (Figure 1c) satisfactorily explains all of the observed spectral features of these bands.