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Updated: May 26, 2025

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
Published on: July 27, 2018
Mass-Selected Infrared Photodissociation Spectroscopic and Theoretical Insights into Nitrobenzene Dimer Anion Tagged
Mingxia Hu1, Yanhui Liu1, Guanjun Wang2
1School of Chemistry and Chemical Engineering & School of Materials Science and Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, China.
Abstract:
The nitrobenzene dimer anion, NB2-, tagged with argon in the gas phase was successfully generated by using a collinear tandem time-of-flight mass spectrometer equipped with a supersonic ion source. Precise characterization was achieved through infrared photodissociation (IRPD) spectroscopy combining with theoretical calculation. Nine distinct absorptions were observed. The optimized structures of NB2(Ar)- were categorized into three types of isomers, including double-hydrogen-bonded (DHB), T-shaped (TS), and antiparallel π-π stacking (APS) isomers. The vibrational analysis indicated that the calculated spectrum of the APS isomer (e) exhibited better agreement with the experimentally observed spectrum than that of the lowest energy DHB isomer (a). Singly occupied molecular orbitals (SOMOs) and natural population analysis (NPA) confirmed that the negative charge in NB2(Ar)- was predominantly localized on one NB unit carrying a charge of -0.932 e, closely resembling a single electron charge. The other NB unit exhibited a minimal negative charge of -0.069 e, and Ar had a charge of 0.001 e. This distribution of charge suggests that NB2- can be viewed as a molecule-anion species, which consists of two separate frameworks: one neutral NB and one anionic NB framework. Energy decomposition analysis (EDA) further revealed that the stabilization of the APS isomer resulted from a nearly equal contribution of dispersion and electrostatic forces. However, for the DHB isomer, only the electrostatic interaction emerged as the primary stabilizing force.
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