METASTABLE STATES OF DIMETHYLAMMONIUM, (CH3)(2)NH2-CENTER-DOT

Hypervalent dimethylammonium radical, (CH3)(2)NH2. and its deuterium-l abeled isotopomers (CH3)(2)ND2., (CH3)(2)NHD., (CD3)(2)NH2. and (CD3)( 2)ND2. were generated as transient species by collisional neutralizati on of their cations in the gas phase and studied by neutralization-rei onization mass spectrometry, laser photoexcitation, and ab initio theo ry. (CH3)(2)ND2., (CH3)(2)NHD., and (CD3)(2)NH2. gave fractions of met astable species of greater than or equal to 3.3 mu s lifetimes, wherea s (CH3)(2)NH2. and (CD3)(2)NH2. dissociated completely on the same tim e scale. Metastable (CD3)(2)NH2. and (CH3)(2)ND2. were photoexcited bu t 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 ((X) over tilde)(2)A(1) ground state of vertic al ionization energy, IEv=3.70 eV. RRKM calculations on the ab initio potential energy surface of the ((X) over tilde)(2)A(1) state predicte d predominant N-H and N-D bond dissociations but did not allow for com petitive loss of CH3 or CD3. The four lowest excited states of (CH3)(2 )NH2., ((A) over tilde)B-2(1), ((B) over tilde)(2)A(1), ((C) over tild e)B-2(2), and ((D) over tilde)(2)A(1), 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 potentia l energy surface crossing of the B and A states and transitions via co nical intersection to the dissociative ground state.