Ab initio calculations, IR, Raman and UV supersonic jet studies of vibrations in 2,6-dicyano-3,5-dimethylaniline

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The infrared and Raman spectra for 2,6-dicyano-3,5-dimethylaniline (DCDMA(NHxD2−x), x=2,1,0) in a solid state and the laser induced fluorescence (LIF) excitation spectra of vacuum isolated jet cooled molecules have been investigated. The ground state S0 and the S1 excited state geometries of DCDMA(NHxD2−x) molecules as well as vibrational frequencies have been evaluated by ab initio calculation using GAUSSIAN94 programs. The DCDMA nonplanar in its ground state S0 (RHF/6-31G*) assumes planar geometry, C2v, in the S1 state (CIS/6-31G*). The correlation between the normal coordinates in different species and in different electronic states has been performed using Dushinsky matrices. The electronic origins were found at 29861cm−1 for DCDMA(NH2), 29852cm−1 for DCDMA(NHD) and 29843cm−1 for DCDMA(ND2). The fundamental frequencies derived from the IR, Raman and LIF excitation spectra have been assigned using the results of ab initio calculations. The scaling factors were found to be 0.890 and 0.846 for the ground state and the singlet excited state frequencies, respectively. The dominant feature of the LIF excitation spectra of DCDMA(NHxD2−x), x=0,1,2, is the presence of a progression in the low frequency mode 5 (112cm−1) involving a symmetrical in-plane motion of the cyano group forming the hydrogen bonds with the amino group.