Contrasting the excited state reaction pathways of phenol and para-methylthiophenol in the gas and liquid phases

摘要: To explore how the solvent influences primary aspects of bond breaking, gas and solution phase photochemistries phenol para-methylthiophenol are directly compared using, respectively, H (Rydberg) atom photofragment translation spectroscopy femtosecond transient absorption spectroscopy. Approaches demonstrated that allow explicit comparisons nascent product energy disposals dissociation mechanisms in two phases. It is found, at least for case weakly perturbing cyclohexane environment, most reaction dynamics isolated molecule reproduced solution. Specifically, phase, both molecules can undergo fast X–H (XO, S) upon excitation with short wavelengths (193 < λpump 216 nm), following population dissociative S2 (11πσ*) state. Product electronic branching, vibrational translational determined. Photolysis 200 nm results formation vibrationally excited radicals on a timescale shorter than fs. Excitation 267 reaches close to S1 (11ππ*)/S2 conical intersection (CI): ultrafast observed systems—again indicating direct potential surface. Comparing this precursor different energies, extent geminate recombination derived H-atom ejection lengths condensed photolyses qualitative agreement release measured studies. Conversely, prepares system its state an well below S1/S2 CI; slow O–H fission inferred experiments time-resolved studies via appearance phenoxyl radical after ∼1 ns, only discernible earlier delay times. The provides additional evidence tunnelling mechanism, where tunnels beneath lower diabats S2/S1 CI. Finally, photodissociation clusters considered, presented coordinate impeded H-bonded dimers.