Metastable States of Dimethylammonium, (CH3)2NH2

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 101; no. 20; pp. 3789 - 3799
• Main Authors: Nguyen, Viet Q, Sadilek, Martin, Ferrier, Jordan, Frank, Aaron J, Tureček, František
• Format: Journal Article
• Language: English
• Published: American Chemical Society 15-05-1997
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp964077e

Hypervalent dimethylammonium radical, (CH3)2NH2 •, and its deuterium-labeled isotopomers (CH3)2ND2 •, (CH3)2NHD•, (CD3)2NH2 •, and (CD3)2ND2 • were generated as transient species by collisional neutralization of their cations in the gas phase and studied by neutralization−reionization mass spectrometry, laser photoexcitation, and ab initio theory. (CH3)2ND2 •, (CH3)2NHD•, and (CD3)2NH2 • gave fractions of metastable species of ≥3.3 μs lifetimes, whereas (CH3)2NH2 • and (CD3)2ND2 • dissociated completely on the same time scale. Metastable (CD3)2NH2 • and (CH3)2ND2 • were photoexcited but not photoionized with the combined 488 and 514.5 nm lines from an Ar-ion laser. Ab initio calculations with effective PMP4(SDTQ)/6-311++G(3df,2p) identified the (X̃)2A1 ground state of vertical ionization energy, IEv = 3.70 eV. RRKM calculations on the ab initio potential energy surface of the (X̃)2A1 state predicted predominant N−H and N−D bond dissociations but did not allow for competitive loss of CH3 or CD3. The four lowest excited states of (CH3)2NH2 •, (Ã)2B1, (B̃)2A1, (C̃)2B2, and (D̃)2A1, were characterized by CIS/6-311++G(3df,2p) calculations, and their vertical ionization energies were calculated as 2.86, 2.57, 2.48, and 1.82 eV, respectively. The excited states were calculated to be strongly bound with respect to N−H bond dissociations. The N−C bond dissociations were interpreted by potential energy surface crossing of the B̃ and à states and transitions via conical intersection to the dissociative ground state.