(a) Calculated minimum energy structures of the parent molecule, CH2ClI, the isomer, CH2Cl–I, and the separated fragments, CH2Cl and I, along with a sketch of the minimum energy path connecting them. The dashed line shows the repulsion from the surrounding matrix schematically. The photolysis pulse (λ photolysis) excites the parent and cleaves the C–I bond, the probe pulse (λ probe) interrogates the isomer, and the recovery pulse (λ recovery) converts the isomer back to the parent. (b) Static electronic absorption spectra of the parent molecule (blue) and of the isomer (red) in a CH4 matrix. The arrows mark the wavelengths of the photolysis, probe, and recovery pulses.
Schematic drawing of the irradiation scheme (top) and the pulse timing diagram (bottom) in the ultrafast experiment. The photolysis and probe pulses cross at a small angle in the sample and the recovery pulse propagates in the opposite direction. The bottom diagram shows a sequence of probe and photolysis pulses. After each probe pulse, a recovery pulse converts a portion of the isomer population back to the parent. After 250 pulse pairs, one of which is darkened in the figure, a fast shutter blocks the photolysis light, and a series of recovery pulses restores the population to within 2% to 3% of its original value.
(a) Minimum energy path from the parent to the two isomers, CH2I–Cl and CH2Cl–I, along with the structures of the isomers and transition states. (b) Fractional contribution of the leading resonance structures from a NBO analysis of the isomers and parent. The covalent structure (black line) is the primary component of the parent. The isomers have a substantial ion-pair component (red line). There is a small ylide component (dashed blue line) in the isomers.
Electronic absorption spectra of the CH2Cl–I isomer in Ar, N2, and CH4 matrices. The maximum moves to successively longer wavelengths for the series of matrices. The vertical arrows mark the probe wavelengths.
Electronic absorption spectrum of the CH2Cl–I isomer in a CH4 matrix and the transient absorption (red points) at the indicated probe wavelengths. The black lines are multiexponential fits to the transient absorption.
Electronic absorption spectrum of the CH2Cl–I isomer in a N2 matrix and the transient absorption (red points) at the indicated probe wavelengths. The black lines are multiexponential fits to the transient absorption.
Electronic absorption spectrum of the CH2Cl–I isomer in an Ar matrix and the transient absorption (red points) at the indicated probe wavelengths. The black lines are multiexponential fits to the transient absorption.
The transient absorption of the CH2Cl–I isomer in a CH4 matrix at four wavelengths along with the multiexponential fits (black lines).
A schematic drawing of the evolution of the CH2Cl–I isomer. After photolysis, the fragments separate and strike the surrounding matrix. The energized fragment can recombine with an iodine atom to form a highly vibrationally excited isomer or to reform the product with characteristic time τ 1. The vibrationally excited isomer subsequently relaxes with characteristic time τ 2.
Time constants and amplitudes of multiexponential fits in CH4, N2, and Ar matrices.
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