Journal
JOURNAL OF PHYSICAL CHEMISTRY A
Volume 125, Issue 16, Pages 3279-3287Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpca.1c00255
Keywords
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Funding
- National Natural Science Foundation of China [22073031, 22027808, U1732146, 22003018]
- Project under Scientific and Technological Planning Grant by Guangzhou City [201805010002]
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This study investigated the neutral and cationic clusters of nitromethane-ammonia using infrared spectroscopy and high-precision quantum chemical calculations. It was found that after ionization, the positive charge redistributes and leads to a proton transfer reaction, which is a result of the highly acidic CH bond caused by hyperconjugation.
It is known that the acidity and reactivity of the CH bond can be enhanced after ionization. Also, this property plays a pivotal role in proton transfer reaction and in the formation of new molecules. Herein, infrared spectroscopy and high-precision quantum chemical calculations are used to study the neutral and cationic clusters of nitromethane-ammonia (CH3NO2-NH3). It is found that in the neutral cluster, CH3NO2 and NH3 are mainly bonded by three intermolecular hydrogen bonds, in which electrostatic contribution plays a major role. After vacuum ultraviolet (VUV) single-photon ionization of CH3NO2-NH3, the positive charge redistributes from the ionized nitrogen atom of NH3 to the CH3NO2 molecule immediately. Then, the proton of CH3NO2 transfers to NH3 to form a proton-transferred type structure CH2NO2-NH4+, without any effective energy barrier, due to the positive hyperconjugation of cationic nitromethane. A closed loop of positive charge transfer takes place in the CH3NO2-NH3 cluster after VUV ionization. The present work demonstrates that both the proton transfer reaction and charge transfer process have occurred in the ionized CH3NO2-NH3 cluster. Moreover, it is found that the proton transfer reaction is a result of the highly acidic CH bond caused by hyperconjugation between the sigma (CH) bond and pi orbital.
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