Knowledge Bank

We have measured the rate of conformational isomerization of 4-chlorobut-1-yne at an energy of $3330cm-1$ 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 $1.2\times 1010s-1$. This rate is more than two orders-of-magnitude slower than the rate calculated using RRKM theory: $1\times 1013s-1$. 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: $3.3\times 108s-1$.