Effect of Spin Multiplicity on Structure, Second Hyperpolarizability and Vibrational Spectrum of Cyanamide

We have investigated the structure, vibrational spectrum and static first (β) and (γ) second hyperpolarizabilities of cyanamide in singlet, triplet and quintet state using Density functional Theory method. The Finite-Field approach has been used to obtain the static first and second hyperpolarizabilities by applying the field in a Z-direction. We have chosen a field strength of 0.008 a.u. to calculate the first and second hyperpolarizabilities of a cyanamide. Cyanamide shows the lowest energy at B3LYP/aug-cc-pvdz level among different levels used here. The geometrical parameter and vibrational frequencies obtain at this level are in close agreement with the experimental determinations. Out of the nine vibrational modes, seven modes in triplet and eight in quintet state are red shifted than those in a singlet state. The only blue shifted mode in quintet is the C N stretching mode with a blue shift of 220 cm^–1 than that for the singlet. The γ values of cyanamide in triplet and quintet state are increased by about 2400 a.u. than the singlet state using electron correlation method. The HOMO–LUMO gap in a singlet state is larger than that for the triplet and quintet state.