Transition States and Nonlinear Excitations in Chloroform Observed with a Sub-5 fs Pulse Laser

Abstract

Sub-5 fs pulse dynamics observed in neat chloroform (CHCl(3)) and the CHCl(3)...O(2) charge-transfer complex in oxygen-saturated chloroform (O(2)-CHCl(3)) were found to be dominated by wave packet motions in the excited state and the ground state, respectively. The time-resolved signal of CHCl(3) exhibits dynamics in the electronic excited state generated by a three-photon absorption process, and that of O(2)-CHCl(3) is explained in terms of the dynamics of the electronic ground state excited by the stimulated Raman process. In addition, we found that the oxidation reaction of chloroform in the charge-transfer complex of chloroform and oxygen easily proceeds via a C-H insertion process triggered by the stimulated Raman process under the irradiation of a visible laser pulse. The spectrogram analysis enabled direct observation of the real-time dynamics of the Raman-triggered oxidation process. These results demonstrate that observation of transition states by sub-5 fs time-resolved spectroscopy is applicable to "ground-state reactions" as well as "excited-state reactions" via stimulated Raman excitation in a wide variety of chemical reactions.