The role of Rydberg states in photoionization of NO2 and (NO+, O-) ion pair formation induced by one VUV photon

TY - JOUR

T1 - The role of Rydberg states in photoionization of NO2 and (NO+, O-) ion pair formation induced by one VUV photon

AU - Poullian, S.M.

AU - Veyrinas, K.

AU - Billaud, P.

AU - Lebech, Morten

AU - Picard, Y.

AU - Lucchese, R.R.

AU - Dowek, D.

PY - 2013/7/28

Y1 - 2013/7/28

N2 - We report a combined experimental and theoretical study of photoionization (PI) of the NO2 molecule into the NO2+ (X 1Σg+) ground state and the photodissociation of NO2 into the NO+(1Σ +) + O-(2P) ion pair. These processes were induced by 10.9 eV-13 eV synchrotron radiation and the products were detected using electron-ion or O--NO+ coincident momentum spectroscopy. The results demonstrate the strong influence of R*(4b 2)-1, nlαi, v2′ Rydberg states vibrationally resolved in the v 2′ bending modes for both processes. In particular, we emphasize two regions around 11.5 eV and 12.5 eV that were studied in more detail for their relevance to 400 nm multiphoton ionization induced by femtosecond pulses. The photoelectron energy spectra and asymmetry parameters support the existence of two PI mechanisms, as probed with the help of fixed-nuclei frozen-core Hartree-Fock calculations. We found significant deviations from Franck-Condon ionization predictions which may be assigned to vibronic coupling of NO2* states such as that induced by a conical intersection. The limited agreement between theory and experiment, even for the non-resonant processes, indicates the need for calculations that go beyond the approximations used in the current study. Ion pair formation leads to strong vibrational and rotational excitation of the NO+( 1Σ+,v) product, with an ion fragment angular anisotropy depending on both the v2′ bending quantum number of the excited parent molecule and the v vibrational level of the fragment.

AB - We report a combined experimental and theoretical study of photoionization (PI) of the NO2 molecule into the NO2+ (X 1Σg+) ground state and the photodissociation of NO2 into the NO+(1Σ +) + O-(2P) ion pair. These processes were induced by 10.9 eV-13 eV synchrotron radiation and the products were detected using electron-ion or O--NO+ coincident momentum spectroscopy. The results demonstrate the strong influence of R*(4b 2)-1, nlαi, v2′ Rydberg states vibrationally resolved in the v 2′ bending modes for both processes. In particular, we emphasize two regions around 11.5 eV and 12.5 eV that were studied in more detail for their relevance to 400 nm multiphoton ionization induced by femtosecond pulses. The photoelectron energy spectra and asymmetry parameters support the existence of two PI mechanisms, as probed with the help of fixed-nuclei frozen-core Hartree-Fock calculations. We found significant deviations from Franck-Condon ionization predictions which may be assigned to vibronic coupling of NO2* states such as that induced by a conical intersection. The limited agreement between theory and experiment, even for the non-resonant processes, indicates the need for calculations that go beyond the approximations used in the current study. Ion pair formation leads to strong vibrational and rotational excitation of the NO+( 1Σ+,v) product, with an ion fragment angular anisotropy depending on both the v2′ bending quantum number of the excited parent molecule and the v vibrational level of the fragment.

U2 - 10.1063/1.4811713

DO - 10.1063/1.4811713

M3 - Journal article

C2 - 23901984

SN - 0021-9606

VL - 139

JO - The Journal of Chemical Physics

JF - The Journal of Chemical Physics

IS - 4

M1 - 044311

ER -