IR MULTIPHOTON DISSOCIATION DYNAMICS OF 2,5-DIHYDROFURAN - TIME-RESOLVED OBSERVATION OF CONCERTED FURAN FORMATION

On infrared multiphoton excitation by a pulsed CO2 laser, vibrationall y excited 2,5-dihydrofuran (DHF) undergoes concerted dissociation gene rating hydrogen and furan as products. The real time evolution of nasc ent furan as a photoproduct is monitored. The formation rate of transi ent vibrationally hot furan, which has an absorption at 245 nm, fits a single exponential with a rate constant (1.8 +/- 0.1) X 10(6) s(-1). An RRKM calculation for the unimolecular dissociation of DHF gives an average energy of DHF as 70.1 +/- 2 kcal/mol corresponding to the expe rimental rates. The nascent hot furan, with a vibrational temperature of 1816 +/- 50 K, exibits a red-shift of 30 nm in the transient absorp tion spectrum.