MODE-SPECIFICITY AND NON-RRKM KINETICS IN THE CONFORMATIONAL ISOMERIZATION OF 4-CHLOROBUT-1-YNE

Author Institution: Department of Chemistry, University of VirginiaWe have measured the rate of conformational isomerization of 4-chlorobut-1-yne at an energy of $3330 cm^{-1}$ above the zero-point level through the rotational spectroscopy of single molecular eigenstates. From the spectrum of the J=3-J=4 rotational transition of several eigenstates in this energy region we measure a unimolecular cunformational isomerization rate of $1.2\times 10^{10} s^{-1}$. This rate is more than two orders-of-magnitude slower than the rate calculated using RRKM theory: $1 \times 10^{13}s^{-1}$. Furthermore, from the eigenstate-resolved rovibrational spectrum of the acetylenic C-H stretch we find that there is strong mode-specificity in the isomerization rate. Coherent preparation of the acetylenic C-H stretch of 4-chlorobut-1-yne leads to even slower isomerization with an upper limit of the rate set by the measured rate of intramolecular vibrational energy redistribution: $3.3\times 10^{8} s^{-1}$