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Issue 4, 2020
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High resolution vibronic state-specific dissociation of NO2+ in the 10.0–15.5 eV energy range by synchrotron double imaging photoelectron photoion coincidence

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Abstract

Vacuum ultraviolet (VUV) photoionization and dissociative photoionization of NO2 in the 10.0–15.5 eV energy range have been investigated in detail by using high-resolution double imaging photoelectron photoion coincidence (i2PEPICO) at synchrotron SOLEIL. Five low-lying electronic states of the NO2+ cation, X1Σg+, a3B2, b3A2, A1A2 and B1B2, are prepared with well-resolved vibronic structures and their state-specific dissociation mechanisms are unraveled and discussed. The present experimental results clarify that except the X1Σg+ ground electronic state and the first three vibrational levels of the a3B2 electronic state, the other cationic states of NO2+ within the present energy range are totally dissociative towards the NO+(X1Σ+) + O(3P) and/or NO+(X1Σ+) + O(1D) dissociation limits. An energy barrier exists along the direct dissociation route of the a3B2 state, and the b3A2 electronic state is a quasi-bound state with a very shallow well, both of which adiabatically correlate to the NO+(X1Σ+) + O(3P) dissociation limit. The a3B2 state mainly with bending vibration excitations undergoes a non-adiabatic transition to the 23A′′(3B1) repulsive state along its bending potential energy curve and then predissociates into the NO+(X1Σ+) + O(3P) products. Our experimental results firstly demonstrate that the NO+(X1Σ+, v) fragment ions produced from individual vibronic levels of the dissociative NO2+(a3B2, b3A2) states are produced at the v = 0 ground vibrational level with a high rotational population due to the excitation of the vibrational bending mode of NO2+ and the associated imparted torque upon dissociation. The slower predissociations of the A1A2 and B1B2 electronic states via their spin–orbit couplings with the repulsive 23A′′(3B1) state produce the NO+(X1Σ+) and O(3P) fragments with a long vibrational progression. In addition, the B1B2 state can also undergo a radiationless transition such as internal conversion into the hot X1Σg+ state and then dissociate into the second dissociation channel correlated to the NO+(X1Σ+) and O(1D) products.

Graphical abstract: High resolution vibronic state-specific dissociation of NO2+ in the 10.0–15.5 eV energy range by synchrotron double imaging photoelectron photoion coincidence

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Article information


Submitted
28 Oct 2019
Accepted
16 Dec 2019
First published
16 Dec 2019

Phys. Chem. Chem. Phys., 2020,22, 1974-1982
Article type
Paper

High resolution vibronic state-specific dissociation of NO2+ in the 10.0–15.5 eV energy range by synchrotron double imaging photoelectron photoion coincidence

X. Tang, G. A. Garcia and L. Nahon, Phys. Chem. Chem. Phys., 2020, 22, 1974
DOI: 10.1039/C9CP05847H

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