Synchrotron based spectroscopic investigation of N,N-dimethylacetamide

Abstract

Spectroscopic investigations are presented for N,N-dimethylacetamide (DMA) in vacuum ultraviolet (VUV) (5–11 eV) and infrared (IR) (570–3200 cm−1) regions. The VUV photoabsorption spectrum of DMA is recorded using synchrotron radiation source. Analysis of experimentally observed spectra is supported with quantum chemical computations. Calculations are performed for geometry optimization of neutral and cationic ground states, molecular orbital plots and potential energy curves of ground and excited states using B3LYP/cc-pVQZ level of theory. Vertical excited singlet and triplet state energies are calculated at the B3LYP/cc-pVQZ and CAMB3LYP/aug-cc-pVTZ levels of theory. Assignments of vibrational bands observed in the IR spectrum are made based on the present computational work and available literature. Experimentally observed peaks in the VUV region are assigned to Rydberg series and valence states by correlating with computed values. Rydberg series for VUV spectrum are extended compared to earlier literature and a few new vibrational assignments are proposed for the IR spectrum. The plots of the PECs for the first few excited states along the various bond lengths show a few avoided crossings of low lying valence and Rydberg states in the Franck-Condon region indicating contribution of Rydberg states in the dissociation dynamics of the molecule on photoexcitation in the VUV region. Present work is a comprehensive spectroscopic study of DMA in the VUV and IR regions.