The electronic structure of the (CN3)(2)N radical and the pyrolysis mechanism of dimethylnitrosamine: A HeI photoelectron spectroscopic study

A continuous dimethylamino (CH3)(2)N +/- (DMA) radical beam is produced in situ by the pyrolysis of dimethylnitrosamine (CH3)(2)NNO at 850 (0.5 degree s C) in a double-heater inlet system on a double-chamber UPS machine-IT whi ch was built specifically to detect transient species. The HeI photoelectro n spectrum (PES) of the (CH3)2N radical is recorded for the first time. To assign the PES bands of the (CH3)2N radical, the improved density functiona l theory (DFT) calculation based on the Amsterdam density functional (ADF) program package has been carried out according to Ct, symmetry for the grou nd state of the neutral (CH3)(2)N radical and the equilibrium geometries of several ionic states of the cationic species. A sharp peak with the lowest ionization energy at 9.01 +/- 0.02 eV comes from electron ionization of th e HOMO(2b(1)) of the (CH3)2N radical, corresponding to the ionization of th e (CH3)2N ((XB1)-B-2) to (CH3)(2)N+(X (1)A(1)). The second band with vibrat ion spacing 1980 +/- 60 cm(-1) comes from electron ionization of 1a(2) orbi tal which is a strongly bound state for the (CH3)(2)N radical, correspondin g to ionization of (CH3)2N (X B-2(1)) to the B-3(1) State of (CH3)(2-) cati on. The PES bands of the NO molecule clearly appears in the PE spectrum of the products pyrolyzed of the compound. The pyrolysis mechanism of the (CH3 )2NNO compound is shown as follows: 850 +/- 0.5 degrees C (CH3)(2)NNO --> ( CH3)(2)N + NO.