Resonance Raman study of the A -band short-time photodissociation dynamics of 2,5-di-iodothiophene

Resonance Raman spectra were obtained for 2,5-di-iodothiophene in cyclohexane solution with excitation wavelengths in resonance with its A -band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion mostly along the nominal symmetric C 2 C 3 ∕ C 4 C 5 stretch ν 2 ( 1388 cm − 1 ) of the thienyl ring and this is accompanied by motions along the nominal symmetric CSC stretch ν 6 ( 640 cm − 1 ) , the nominal symmetric C  I stretch ν 7 ( 187 cm − 1 ) , the nominal antisymmetric CSC stretch ν 19 ( 728 cm − 1 ) , the nominal antisymmetric C 2 C 3 ∕ C 4 C 5 stretch ν 16 ( 1497 cm − 1 ) , the nominal C 3 C 4 stretch ν 3 ( 1286 cm − 1 ) and four other vibrational modes. A preliminary resonance Raman intensity analysis was done and the results for 2,5-di-iodothiophene were compared to previous results for 2-iodothiophene and di-iodomethane to discuss the mechanism of the symmetric breaking in the initial A -band photodissociation dynamics of 2,5-di-iodothiophene and 2-iodothiophene.