Fig. 8.

PIE curve (top) and threshold photoelectron spectrum (TPES, bottom) of the m/z=57 signal (butyl radicals) obtained from the reaction zone of a fuel-rich isobutane flame. Signals are compared to the adiabatic (top panel and dashed lines) and vertical (bottom) ionization thresholds (IP) and photoelectron spectra (PES) of tert-butyl (solid, red line), iso-butyl (dotted, green line), 1-butyl (solid, blue line), and 2-butyl (dotted, yellow line). Literature for the reference PES is given in the original article. Reprinted from [99] with the permission of AIP Publishing.