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Description:
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The vibrational potential energy surfaces in electronic ground and excited states of several ring molecules were investigated using several different spectroscopic methods , including far -infrared (IR ) , Raman , ultraviolet (UV ) absorption , fluorescence excitation (FES ) , and single vibronic level fluorescence (SVLF ) spectroscopies . Based on new information obtained from SVLF and millimeter wave spectra , the far -IR spectra of coumaran were reassigned and the one -dimensional ring -puckering potential energy functions for several vibrational states in the S0 ground state were determined . The barrier was found to be 154 cm -1 and the puckering angles to be à ± 25à ° , in good agreement with the millimeter wave barrier of 152 cm -1 and puckering angles of à ± 23à ° . Moreover , the UV absorption and FES spectra of coumaran allowed the one -dimensional ring -puckering potential energy functions in the S1 excited state to be determined . The puckering barrier is 34 cm -1 for the excited state and the puckering angles are à ± 14à ° . Several calculations with different basis sets have been carried out to better understand the unusual vibrational frequencies of cyclopropenone . It was shown that there is strong interaction between the C=O and symmetric C -C stretching vibrations . These results differ quantitatively from a previous normal coordinate calculation and interpretation . The vapor -phase Raman spectrum of 3 ,7 -dioxabicyclo[3 .3 .0]oct -1 ,5 -ene was analyzed and compared to the predicted spectrum from DFT calculations . The spectrum further shows it has D2h symmetry , in which the skeletons of both rings are planar . The infrared and Raman spectra of vapor -phase and liquid -phase 1 ,4 -benzodioxan and 1 ,2 ,3 ,4 -tetrahydronaphthalene were collected and the complete vibrational assignments for both molecules were made . Theoretical calculations predicted the barriers to planarity to be 4809 cm -1 for 1 ,2 ,3 ,4 -tetrahydonaphthalene and 4095 cm -1 for 1 ,4 -benzodioxan . The UV absorption , FES , and SVLF spectra of both molecules were recorded and assigned . Both one and two -dimensional potential energy functions of 1 ,4 -benzodioxan for the ring -twisting and ring -bending vibrations were carried out for the S0 and S1 (à  ,à  * ) states , and these were consistent with the high barriers calculated for both states . The low -frequency spectra of 1 ,2 ,3 ,4 -tetrahydronaphthalene in both S0 and S1 (à  ,à  * ) states were also analyzed . |