The hydride abstraction reaction in the Mg+-NH2CH3 complex has been investigated by using the DFT and MP2 methods. Two local minima and two transition states have been found along the reaction pathway. Accompanied with IRC calculations, the reaction is revealed to be a three-step process, i. e., a hydrogen-migration process followed by a charge-transfer process and a nonreactive-dissociation process. On the basis of single-point calculations using CCSD (T) in conjunction with 6-311++G (d, pd) basis set with the geometries optimized at B3LYP/6-311++G** with zero point energy (ZPE) corrections, the reaction energies for all the steps are predicted.

aneous rupture of both bonds. The action spectrum consists of two broad peaks between the atomic transition of Mg+(3 2P←3 2S). Ab initio calculations show a minimum-energy structure, in which Mg+ attaches to the O atom and one of the three F atoms of 2,2,2-trifluoroethanol, forming a five-membered ring. The calculated absorption spectrum corresponding to the minimum-energy structure agrees nicely with the experimental action spectrum. The branching fractions of the photoproducts are approximately constant in a given spectral range, but they change significantly across the spectral ranges. The constant branching fractions point to the ground state reactions following traversals from the initially accessed excited states through conical intersections. On the other hand, the observation of the electronic state-specific branching fractions is explained by the orbital alignments of the excited electron, which is dictated by the five-membered ring structure of the complex.

The resonance-enhanced multip hoton ionization (REMPI) spect rum of 2-but anone in 467～488nm was obt ained using multiphoton ionization-time-of-flight mass spect rometric technique and dye laser. By analyzing the spectrum, we have ascert ained that thest rongest peak in the REMPI spectrum, 62305cm-1, could be at tributed to one component of the 3d Rydberg transition, the peaks in 63291～63898cm-1 are mixed Rydberg-valence vibronic transitions, and 63291cm-1 is the 0-0 transition of the state.

Photoinduced reactions in Mg+-NH2CH3 and Mg+-NH (CH3)2 have been studied in the spectral range of 230-440nm. Although the N-H bond activation channel was found to be prominent in the photodissociation of Mg+-NH3 [Yoshida, Okai, and Fuke, Chem. Phys. Lett. 347, 93 (2001)], it is very unfavorable as the ammonia is replaced by methylamines in the complex. Instead, C-H bond cleavage products are observed from Mg+-NH(CH3)(CH2NH2+) and exclusively produced from Mg+-NH(CH3)2((CH3) HN+=CH2) after photoexcitation. For Mg+-NH2CH3, the C-N bond activation product Mg+NH2 and the charge transfer product CH3NH2+ are also abundant. The action spectra of the 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 are in good agreement with the observed action spectra. On the basis of the branching fraction data and the calculated complex structures, the C-H bond activation is invoked to account for the MgH loss channel after photoexcitation, followed by a nonadiabatic transition to the ground state by a bond-stretch mechanism. However, the formation of Mg1NH2 from photodissociation of Mg+-NH2CH3 involves the insertion of Mg1 into the C-N bond. Finally, the photoinduced charge transfer product CH3NH21 are also identified from Mg+-NH2CH3 but not from Mg+-NH (CH3)2.

Photodissociation spectroscopy of the Mg+-pyridine complex in the spectral range of 240-440 nm is presented in the paper. Mass spectrometry of the complex exhibits the persistent product Mg+ from non-reactive quenching throughout the whole wavelength range. A minor charge transfer (CT) product C5H5N+ is also observed when the laser wavelength is shorter than 249nm. The action spectrum of the complex was recorded as a function of laser wavelength. Three pronounced bands with a symmetrical feature were observed in the action spectrum. The optimized geometry of Mg+-pyridine is characterized by the linkage of Mg+ to the N atom of the molecule possessing a C2v symmetry with Mg on the C2 axis of the complex. The calculated vertical absorption spectrum of the complex using the optimized structure of its ground state agrees qualitatively with the observed action spectrum. The relative yield of the CT product shows a threshold feature and rises with the shortening of the laser wavelength. The action spectrum of the CT product has a nearly similar feature to that of the total ion in the wavelength range of 240-250nm. Based on the experimental results, the predissociative CT reaction mechanism is invoked to account for the yield of the photoinduced CT product C5H5N+.

Photoinduced reactions have been systematically studied on mass-selected complexes of Mg+ with tri-and tetrasubstituted benzene by F and/or CH3. The complexes fall into two groups. The Group I complexes involve bidentate coordination of the o-F atoms to Mg+, whereas the Group II complexes feature the linkage of Mg+ to only one of the F atoms. The o-benzyne radical cations were found to be the predominant photolysis products from the Group I complexes, but the yields of the benzyne radical cation products were low for Group II. For each group of complexes, different substituents, including CH3 (medium

Acetonitrile-solvated Mg+ complexes Mg+(NCCH3)n were produced in a pick-up source. The Mg+(NCCH3)n clusters were subjected to photodissociation in a time-of-flight reflectron mass spectrometer. Except for a minor reactive product Mg1-NC at short wavelengths, only nonreactive (or evaporation) fragments were observed from photodissociation of Mg1 (NCCH3) n (n=1-4). Action spectra of Mg+(NCCH3)n (n=1-4) were recorded in the spectral region of 230-560nm, which provide insight into the structure and photodissociation dynamics of the complexes. For all the complexes we studied, the ligands are believed to be in the first solvation shell. Both the evaporation and reaction processes occur on the ground state surfaces of the complexes. By using the DFT/B3LYP and CIS methods, the most stable ground-state structures and the excitation spectra for Mg+(NCCH3) 1-3 were obtained. The ab initio predictions appear to be consistent with the experimental results.

Distonic o-, m-, and p-benzyne radical cations (1-3) have been generated by a novel photolysis reaction of mass-selected Mg+-difluorobenzene complexes. The energy required for the formation of these radical cations is within 2.2 eV. The formation of o-benzyne cation is most facile. The benzyne radical cations dissociate further to yield ethyne and 1, 3-butadiyne radical cation as major products given a sufficient amount of energy. The whole process involves only a single photon, and is very efficient. The calculated threshold for the formation of 1, 3-butadiyne radical cation from Mg+(o-C6H4F2) is about 4.6eV, quite comparable with the experimental estimate.

We present the photodissociation spectroscopy of the complexes of Mg+ with di- and tri-ethylamine in the spectral range of 230-440nm. 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 Mg1 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 a-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.

The decarbonylation of acetaldehyde assisted by Co+, which was selected as a representative system of the transition metal ions-assisted decarbonylations of acetaldehyde, has been investigated using density functional theory at the B3LYP/6-31+G** level of theory. The geometries and energies of the reactants, intermediates, products and transition states relevant to the reaction were located in detail on the triplet ground potential energy surfaces of [Co, O, C2, H4]+. Our calculations indicate the decarbonylation of acetaldehyde takes place through three steps, that is, C-C activation, aldehyde H-shift and nonreactive dissociation, while C-H activation by Co+ can't lead to the decarbonylation of acetaldehyde. The stable precursor of the decarbonylation products is determined to have a structure of (CH4) Co+(CO) rather than (CH3) HCo+(CO) proposed by earlier researchers [refs. 1,2].