Using isotopologues to probe the potential energy surface of reactions of CH +CH.

Investigations into bimolecular reaction kinetics probe the details of the underlying potential energy surface (PES), which can help to validate high-level quantum chemical calculations. We utilize a combined linear Paul ion trap with a time-of-flight mass spectrometer to study isotopologue reactions between acetylene cations (CH ) and two isomers of CH: propyne (HCH) and allene (HCH). In a previous study [Schmid et al.

Time-Resolved Photochemistry of Stiffened Stilbenes.

Broadband transient absorption spectroscopy is used to study the photoisomerization of stiffened stilbenes in solution, specifically E/ Z mixtures of bis(benzocyclobutylidene) (t4, c4) and ( E)-1-(2,2-dimethyltetralinylidene)-2-2-dimethyltetraline (t6). Upon excitation to S, all evolve to perpendicular molecular conformation P, followed by decay to S, while the spectra and the kinetic behavior crucially depend on the size of the stiffening ring. In 4, contrary to all previously studied stilbenes, the trans and cis absorption and excited-state spectra are nearly indistinguishable, while the corresponding isomerization times are comparable: τ = 166 ps for t4 and τ = 64 ps for c4 in n-hexane, as opposed to 114 and 45 ps in acetonitrile, respectively.