Imaging studies of the multiphoton excitation, dissociation and ionization of Br2

Abstract

Both ions and photoelectrons arising in the multiphoton excitation of molecular bromine at various wavelengths in the range 430–475 nm have been investigated using imaging methods. The ion time-of-flight (TOF) spectra show only Br⁺ fragment ions (and no parent ions) under the prevailing experimental conditions. However, analysis of the photoelectron images shows clear evidence of both parent ion formation and predissociation at the energy of four absorbed photons. Highly excited Br atoms in the ⁴P_1/2 and/or ²P_3/2 states derived from the electronic configuration ···4s²4p⁴[³P₁]5s (with respective term values of 66883.9 and 67183.6 cm⁻¹) are amongst the predissociation products. Analysis of the ion images reveals efficient one (and two) photon excitation and dissociation of the parent Br₂⁺ ions (depending on excitation wavelength and the extent of internal excitation within the parent ion)—thereby accounting for the observed absence of parent ions in the ion TOF spectrum. The study also serves to reinforce previous conclusions regarding spin–orbit branching in the Br atomic fragments resulting from one photon dissociation of Br₂ in this wavelength range, and provides tantalizing glimpses of the rich variety of multiphoton ionization dynamics exhibited by the atomic Br fragments.