Femtosecond dynamics of cyclopropenylidene, c-C₃H₂

Abstract

The photophysics of the B (1)B(1) state of isolated cyclopropenylidene, c-C(3)H(2), has been studied by femtosecond time-resolved photoionisation and photoelectron spectroscopy. The carbene was produced by flash pyrolysis of 3-chlorocycloprop-1-ene. The bands at 266.9 nm and 264.6 nm have been investigated. The excited state deactivates in a two step process. The first time constant of less than 50 fs corresponds most likely to a nonradiative transition to the A-state, the second one on the order of 200 fs describes the internal conversion to the electronic ground state. The data are compared to those measured for the chlorinated carbene c-C(3)HCl. In the photoelectron spectrum of c-C(3)H(2) resonances were observed which can be assigned to members of a Rydberg d-series.

Photodissociation Dynamics of Cyclopropenylidene, c‐C3H2

“…The values of the internal coordinates for all optimized geometries are given in the Supporting Information. As evinced by the figure, the computed vertical excitation energy to the bright S 2 ( 1 B 1 ) state, corresponding to the second band in Figure 3, is 4.70 eV, which is equal to the energy of the 267 nm pump pulse employed in the fs‐experiments 15. The value is in very good agreement with the previously computed values of 4.7414 and 4.89 eV 19d.…”

“…We therefore carried out computations to provide insight into the short‐time processes and to support the experimental data. The results are compared below to the earlier fs‐photoionization study 15…”

“…The results are compared below to the earlier fs-photoionization study. [15] Potential-energy surfaces Ab initio optimized structures relevant to the excited state dynamicsa re presented in Figure 4, as is the atom labelling that will be employed in the following discussion. The values of the internal coordinates for all optimized geometriesa re given in the Supporting Information.…”

“…[13] The brightB 1 B 1 state was identified by multiphoton ionization, [14] and its ultrafast internal conversion was followed by femtosecond (fs-) photoelectron spectroscopy. [15] SubsequentH -atom loss was observed by photofragmente xcitation spectroscopy, but neither ap roduct-energy distribution nor mechanistic details have been reported.W et herefore initiated as tudy using velocity map imaging (VMI). [16] In previous experiments on 1, mostly chlorocyclopropene, c-C 3 H 3 Cl was used as the precursor.…”

“…The ground state is the 1 A 1 , as both carbene electrons are in a σ orbital, resulting in 2π electrons and engendering an aromatic ring 13. The bright B 1 B 1 state was identified by multiphoton ionization,14 and its ultrafast internal conversion was followed by femtosecond (fs‐) photoelectron spectroscopy 15. Subsequent H‐atom loss was observed by photofragment excitation spectroscopy, but neither a product‐energy distribution nor mechanistic details have been reported.…”