화학공학소재연구정보센터
Journal of Chemical Physics, Vol.110, No.18, 8954-8968, 1999
Electronic accessibility of dissociation channels in an amide: N,N-dimethylformamide photodissociation at 193 nm
Measurement of the photofragment velocity and angular distributions from the photodissociation of N,N-dimethylformamide at 193 nm in its pi(nb)pi* absorption evidences three competing dissociation channels: HCON(CH3)(2) --> HCO((X) over tilde (2)A') + N(CH3)(2)((X) over tilde B-2(1)); HCO((X) over tilde (2)A') + N(CH3)(2)((A) over tilde (2)A(1)); and HCONCH3 + CH3. (H atom eliminations are not probed.) These products are formed in a ratio of 0.15 +/- 0.04: 0.49 +/- 0.09: 0.36 +/- 0.07, determined by use of trimethylamine as a calibrant molecule. Nitrogen-carbonyl bond fission occurs on a rapid time scale with an angular distribution of the dissociation products given by beta = 1.2 +/- 0.2. Excited state N(CH3)(2) products are formed quasidiabatically from the initial planar geometry, whereas symmetry-breaking vibrations allow one-electron matrix elements to couple the initial electronic configuration to the ground state N(CH3)(2) + HCO channel. Competition of nitrogen-methyl bond fission is evidence of the strong coupling between the pi(nb)pi* excitation and the nitrogen-methyl reaction coordinate; ab initio calculations confirm that the electronic excitation is not localized on the N-C=O moiety. We also include here an advance report of the excited state energy of the N(CH3)(2)((A) over tilde(2)A(1)) radical, which is found to be 1.59 eV.