Femtosecond real-time probing of reactions. IX. Hydrogen-atom transfer
نویسندگان
چکیده
The real-time dynamics of hydrogen-atom-transfer processes under collisionless conditions are studied using femtosecond depletion techniques. The experiments focus on the methyl salicylate system, which exhibits ultrafast hydrogen motion between two oxygen atoms due to molecular tautomerization, loosely referred to as intramolecular “proton” transfer. To test for tunneling and mass effects on the excited potential surface, we also studied deuterium and methyl-group substitutions. We observe that the motion of the hydrogen, under collisionless conditions, takes place within 60 fs. At longer times, on the picosecond time scale, the hydrogen-transferred form decays with a threshold of 15.5 kJ/mol; this decay behavior was observed up to a total vibrational energy of -7200 cm-‘. The observed dynamics provide the global nature of the motion, which takes into account bonding before and after the motion, and the evolution of the wave packet from the initial nonequilibrium state to the transferred form along the O-H-O reaction coordinate. The vibrational periods (2?r/w) of the relevant modes range from 13 fs (the OH stretch) to 190 fs (the low-frequency distortion) and the motion involves (in part) these coordinates. The intramolecular vibrationalenergy redistribution dynamics at longer times are important to the hydrogen-bond dissociation and to the nonradiative decay of the hydrogen-transferred form.
منابع مشابه
Femtosecond real‐time probing of reactions. XXI. Direct observation of transition‐state dynamics and structure in charge‐transfer reactions
متن کامل
Femtosecond real-time probing of reactions. VIII. The bimolecular reaction Br+I2
In this paper, we discuss the experimental technique for real-time measurement of the lifetimes of the collision complex of bimolecular reactions. An application to the atom-molecule Br + I, reaction at two collision energies is made. Building on our earlier Communication [J. Chem. Phys. 95, 7763 ( 1991)], we report on the observed transients and lifetimes for the collision complex, the nature ...
متن کاملFemtosecond probing of bimolecular reactions: The collision complex
Progress has been made in probing the femtosecond dynamics of transition states of chemical reactions.* The “half-collision” case of unimolecular reactions has been experimentally investigated for a number of systems and much theoretical work has already been developed.2 For bimolecular reactions, the case of full collision, the zero of time is a problem which makes the femtosecond temporal res...
متن کاملComparison of hydride, hydrogen atom, and proton-coupled electron transfer reactions.
A comparison of hydride, hydrogen atom, and proton-coupled electron transfer reactions is presented. Herein, hydride and hydrogen atom transfer refer to reactions in which the electrons and protons transfer between the same donor and acceptor, while proton-coupled electron transfer (PCET) refers to reactions in which the electrons and protons transfer between different centers. Within these def...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 1999