On the adiabatic ionization energy of the propargyl radical.

The photoionization and pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the propargyl radical have been recorded in the vicinity of the origin of the X(+) (1)A1←X(2)B1 photoionizing transition. An internally cold sample of propargyl with a rotational temperature of ~45 K was produced in a supersonic expansion of 1,3-butadiene in helium. Propargyl was generated by excimer laser (ArF, 193 nm) photolysis of 1,3-butadiene in a quartz capillary mounted at the exit of a pulsed valve. The rotational structure of the origin band of the photoelectron spectrum was partially resolved and an improved value of the adiabatic ionization energy of propargyl (E(I)/hc = 70174.5(20) cm(-1)) was determined.