Emission and laser-induced excitation spectra of rotationally cooled perfluoro-2,4-hexadiyne cation (Ã2Eu↔X2Eg) and photoelectron–photon coincidence studies of the Ã2Eu state

Abstract

The òE_u↔X²E_g band system of rotationally and vibrationally cooled perfluoro-2,4-hexadiyne cation has been studied by emission and excitation spectroscopies. The emission spectrum was obtained by electron-impact excitation of a seeded supersonic free jet and the excitation spectrum by laser-induced fluorescence on cations produced by Penning ionisation. From these spectra the vibrational frequencies of the totally symmetric fundamentals could be inferred for the X²E_g and òE_u state to an accuracy of ±2 or ±5 cm^–1, respectively. The relaxation behaviour of the excited cation has been quantitatively followed by photoelectron–photon coincidence measurements. These yield fluorescence quantum yields and lifetimes of the state-selected cation and hence the radiative and radiationless rate constants of the decay channels.