No Access Submitted: 13 May 2014 Accepted: 16 July 2014 Published Online: 04 August 2014
J. Chem. Phys. 141, 054201 (2014);
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  • Dan J. Harding
  • J. Neugebohren
  • M. Grütter
  • A. F. Schmidt-May
  • D. J. Auerbach
  • T. N. Kitsopoulos
  • A. M. Wodtke
We present a new photo-fragment imaging spectrometer, which employs a movable repeller in a single field imaging geometry. This innovation offers two principal advantages. First, the optimal fields for velocity mapping can easily be achieved even using a large molecular beam diameter (5 mm); the velocity resolution (better than 1%) is sufficient to easily resolve photo-electron recoil in (2 + 1) resonant enhanced multiphoton ionization of N2 photoproducts from N2O or from molecular beam cooled N2. Second, rapid changes between spatial imaging, velocity mapping, and slice imaging are straightforward. We demonstrate this technique's utility in a re-investigation of the photodissociation of N2O. Using a hot nozzle, we observe slice images that strongly depend on nozzle temperature. Our data indicate that in our hot nozzle expansion, only pure bending vibrations – (0, v2, 0) – are populated, as vibrational excitation in pure stretching or bend-stretch combination modes are quenched via collisional near-resonant V-V energy transfer to the nearly degenerate bending states. We derive vibrationally state resolved absolute absorption cross-sections for (0, v2 ≤ 7, 0). These results agree well with previous work at lower values of v2, both experimental and theoretical. The dissociation energy of N2O with respect to the O(1D) + N2Σg+1 asymptote was determined to be 3.65 ± 0.02 eV.
This work is sponsored by Deutsche Forschungsgemeinschaft and the Alexander von Humboldt Professorship. A.M.W., T.N.K., and M.G. would like to acknowledge support from the Alexander von Humboldt Foundation. We thank Mr. Florian Lange for outstanding technical support. We also thank Professor Dr. R. Schinke for enlightening discussions concerning the photodissociation of N2O and Dr. Bérenger Gans, Université Paris-Sud, for helpful discussions in the design and building of the Chen-pyrolysis source.