The pulsed-field ionization zero-electron kinetic-energy (PFI-ZEKE) threshold photoionization spectrum of NO2 from 9.58 to 20 eV is obtained using vacuum ultraviolet synchrotron radiation by means of the Chemical Dynamics Beamline at the Lawrence Berkeley National Laboratory Advanced Light Source. The high resolution afforded by PFI threshold discrimination yields new or refined spectroscopic constants for a number of known excited states of the cation, including the first estimate of the A rotational constant in the a 3B2 state, as well as new fundamental frequencies for the A 1A2 and B 1B2 states, a precise determination of the singlet–triplet splitting in the c 3B1–C 1B1 complex and the first observations of the states, d 3A1 and D 1B2. Most significantly, ZEKE photoelectron detection resolves vibrational structure in the linear X 1Σg+ ground state of NO2+. Vibrational positions in the first electron volt of the spectrum are found to conform with the predictions of a Hamiltonian that includes Fermi resonance and other anharmonic terms derived from earlier multiresonant laser spectroscopic experiments on the lower bending excited states.

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