Threshold photoelectron spectroscopy of small organo-selenium radicals

Abstract

We present threshold photoelectron spectra of several reactive selenium-containing intermediates generated by pyrolysis of dimethyldiselenide, (CH₃)₂Se₂. The detected species include CH₃Se₂, Se₂ and CH₃Se radicals. Short-lived intermediates were produced in situ using a heated microreactor and characterized via mass-selected threshold photoelectron spectroscopy, using synchrotron radiation at the Swiss Light Source and a photoelectron–photoion coincidence (PEPICO) detection scheme. The data yield ionization energies for the transition into the ionic ground state of 8.28 eV ((CH₃)Se₂), 8.85 eV (Se₂) and 8.92 eV ((CH₃)Se). The values are accurate within ±10 to ±20 meV. In addition, transitions into excited electronic states of the ion were also investigated. Simulations of the vibrational structure based on quantum chemical calculations provide further insight into structural changes upon ionization. By directly comparing these results to previously studied sulfur and oxygen analogues, we identify both similarities and key differences in the bonding and fragmentation behavior of group 16 radicals.