Photodissociation of Mg+-XCH3 (X=F, Cl, Br, and I) complexes. II. Fragment angular and energy distributions

Ari Furuya, Fuminori Misaizu, Koichi Ohno

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Angular and energy distributions of photofragments from Mg +-XCH3 (X=F, Cl, Br, and I) were deduced from time-of-flight (TOF) profiles measured by rotating the polarization direction of the dissociation laser with respect to ion beam direction. The TOF profiles of ICH3+ and MgI+ fragment ions produced from Mg+-ICH3 complex with 266 and 355 nm photons showed clear but opposite recoil anisotropy to each other. In addition, BrCH3 + formed by a dissociation of the Mg+-BrCH3 complex at a photolysis wavelength of 266 nm also showed an anisotropic distribution in the TOF profile which had the same behavior as the profile of ICH3+. For Mg+-FCH3 complex, CH 3+ and MgF+ formed with a 266 nm photon had also spatial anisotropy, in which the TOF profile of MgF+ was almost opposite to that of MgI+. These anisotropic distributions were explained by (1) local excitation on the Mg+ ion, (2) rapid dissociation compared with a rotational period of the parent complex, and (3) geometrical structures of the parent complexes. Anisotropy β parameter values were determined to be + 1.30(ICH3+), -0.50(MgI +), +0.74(BrCH3+), and +0.75(CH 3+ and MgF+). This dependence on the halogen atom observed in β values was qualitatively explained by both the geometrical parameters and classical rotational periods of parent complexes. In the product energy distribution, 46%, 40%, 21%, 16%, and 16% of available energies were found to be transferred into translational energies of ICH 3+, MgI+, BrCH3+, CH 3+, and MgF+, respectively. These values were compared with energy distributions estimated by a statistical prior distribution and a nonstatistical impulsive model. For ICH3+ and MgI+, the translational energies determined from the measurement had values between those estimated from statistical and nonstatistical models. On the other hand, the energy partitioning for the product ions of BrCH 3+, CH3+, and MgF+ was found to be almost statistical. From these considerations, we concluded that nonstatistical processes were more important in the dissociation of Mg +-ICH3 than in other systems.

Original languageEnglish
Article number094310
JournalJournal of Chemical Physics
Issue number9
Publication statusPublished - 2006


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