Excited-state lifetime of propadienylidene, l-C3H2

Abstract

The excited-state dynamics of the singlet carbene propadienylidene, l-C₃H₂, were investigated by femtosecond time-resolved photoionisation. The carbene was excited into the C ¹A₁ state with 250 nm pulses and the subsequent excited state dynamics were probed by multiphoton ionization with 800 nm pulses. The lifetime of the C ¹A₁ state was determined to be 70 fs. In agreement with recent nanosecond experiments, we assume that the carbene deactivates to the electronic ground state where it subsequently dissociates. Since propadienylidene was generated from 3-bromo-1-iodopropyne, two further radical intermediates were studied, IC₃H₂ and C₃H₂Br. For both species, an ultrafast excited state decay was observed with an upper limit of 40 fs for the respective lifetimes.