Theoretical studies on the low-lying electronic states of the diazomethyl (HCNN) radical and its ions

The diazomethyl (HCNN) radical has attracted considerable attention due to its great interest in interstellar chemistry and combustion processes. In this article, we have systemically studied the low-lying electronic states of the HCNN radical and its ions through complete active space self-consistent field and multiconfigurational second-order perturbation theory. For the ground state of HCNN, the calculated CH stretch ν1, asymmetric NNC stretch ν2, and NCH bend ν4 are 3305, 1876, and 870 cm−1, respectively. The ν4 is close to the experimental value of 871 cm−1. The adiabatic excitation energies of 12A′ and 22A″ of HCNN are shown to be in agreement with the experimental reports. Moreover, the first adiabatic detachment energy of HCNN− is 1.628 eV, which accords with the experimental value of 1.685 ± 0.006 eV. Our work might not only be helpful for deeply understanding the character of the low-lying electronic states of the HCNN radical and its ions, but also provide a theoretical guidance for further studying the photoelectron spectrum of HCNN and HCNN−.