A characterization of vibrationally and electronically excited NO2+ by high-resolution threshold photoionization spectroscopy

The pulsed-field ionization zero-electron kinetic-energy (PFI-ZEKE) thresho ld photoionization spectrum of NO2 from 9.58 to 20 eV is obtained using vac uum ultraviolet synchrotron radiation by means of the Chemical Dynamics Bea mline at the Lawrence Berkeley National Laboratory Advanced Light Source. T he high resolution afforded by PFI threshold discrimination yields new or r efined spectroscopic constants for a number of known excited states of the cation, including the first estimate of the A rotational constant in the a B-3(2) state, as well as new fundamental frequencies for the A (1)A(2) and B B-1(2) states, a precise determination of the singlet-triplet splitting i n the c B-3(1)-C B-1(1) complex and the first observations of the states, d (3)A(1) and D B-1(2). Most significantly, ZEKE photoelectron detection res olves vibrational structure in the linear X (1)Sigma(g)(+) 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 las er spectroscopic experiments on the lower bending excited states. (C) 1999 American Institute of Physics. [S0021-9606(99)00444-4].