Resolving the controversy over the second ionization potential of the nitrate free radical NO3

Two experimental studies determining the ionization potentials (IPs) of a n itrate free radical have recently been done. The first study performed usin g discharge flow-photoionization mass spectroscopy (PIMS) determined the ad iabatic ionization potential at 12.57 eV. The second study using the HeI ph otoelectron spectroscopy (PES) observed five bands with the five lowest ver tical ionization potentials of NO3 at 12.55, 13.18, 13.62, 14.05, and 15.54 eV. The second IP determined using PES (at 13.18 eV) has been questioned d ue to its absence in the spectrum obtained using the PIMS experiment. We us e our theoretical method, the multiconfigurational spin tensor electron pro pagator method (MCSTEP), to help resolve the controversy over the ionizatio n potential of NO3. We perform MCSTEP calculations on NO3 using the standar d cc-pVDZ and cc-pVTZ basis sets at D-3h and C-2v geometries. Our results a t both of these two symmetries support the experimental results obtained us ing PES. (C) 2000 American Institute of Physics. [S0021-9606(00)30610-9].