Photodissociation spectroscopy of the complexes of Mg+ with di- and tri-ethylamine

Abstract

We present the photodissociation spectroscopy of the complexes of Mg+ with di- and tri-ethylamine in the spectral range of 230–440 nm. Mass spectrometry of the two parent complexes exhibits the persistent product Mg+ from nonreactive quenching throughout the whole wavelength range. As for the reactive channels, C3H7•-elimination products are dominant when the complexes are excited to 3Px,y. Furthermore, photoexcitation of Mg+–NH(C2H5)2 to 3Px,y yields a minor MgH-elimination fragment. On the other hand, photodissociation of Mg+–N(C2H5)3 produces charge-transfer fragments N+(C2H5)3 and (C2H5)2N+CH2. The action spectra of the two complexes consist of two pronounced peaks on the red and blue side of the Mg+ 3 2P←3 2S atomic transition. The calculated absorption spectra of the two complexes using the optimized structures of their ground states agree nicely with the observed action spectra. Photofragment branching fractions of the products are shown to be nearly independent of the photon energy for the 3Px,y excitation, indicating the importance of exit channel effects. A photoreaction mechanism is proposed for C3H7•-elimination, which entails Mg+ insertion into one C–N bond, followed by a nonadiabatic transition to the ground-state surface through a conical intersection. However, for the MgH-elimination channel in the photodissociation of Mg+–NH(C2H5)2, Mg+ rather inserts into the α-C–H bond. Finally, photoexcitation of Mg+–N(C2H5)3 leads to a prominent charge-transfer product [N+(C2H5)3]*, which dissociates further to (C2H5)2N+CH2 by a loss of CH3•.