Raw velocity mapped ion images of atoms with low kinetic energy produced by the photodissociation of free molecules and by van der Waals complexes at : crushed (left) and sliced (right) images of (a) free , (b) , (c) , (d) , and (e) . Signal from excess free has not been subtracted from the images. In the upper right corner the enumerated channels C1–C5 observed in the images (Figs. 1 and 2) of the studied complexes as well as from free molecules (C0) are schematically shown. Vector shows the direction of the polarization of the exciting radiation. For the and complexes, a high kinetic energy channel C5 was also observed (see Fig. 2).
Raw slice images of atoms produced in the photodissociation of the van der Waals complexes (a) with probed, (b) with probed, and (c) with probed. Images (a) and (c) are the same as the sliced images on Figs. 1(e) and 1(d), respectively, but with a larger part of the image shown to include the outer ring. This outer ring for all of the images has been artificially enhanced in intensity by a factor of 5–10 for better visibility in this figure.
Speed distributions of atoms arising from the photodissociation of (a) , (b) , (c) , and (d) . The speed distribution for atoms from free molecules is also presented for comparison. The distributions are derived by inversion of the crushed velocity map images. The anisotropy parameters taken at the maxima of the distributions are shown on the images and denoted as . The anisotropy of the channel C5 is also shown in Figs. 3(a) and 3(b).
Calculated structures of the isomers of the van der Waals complex. Four types of isomers are found to exist, with geometry parameters shown in the table inset. All of these forms have symmetry and a degeneracy factor of 3 corresponding to rotation of the subunit around the axis of the subunit by 120°. For the form shown, the symmetry plane coincides with the plane of the figure and so one of the H atoms is screened by the atom . The vector connecting the I atom and the center of mass of the subunit is almost perpendicular to the O–O bond in all of the isomers. In all of these structures the ground state of the complex has symmetry. The numbers marked in bold correspond to the isomer with the shortest distance for which the properties of the charge-transfer electronic excited state have then been calculated (see text).
Potential energy curves for the electronic states of van der Waals complexes. The curves corresponding to the covalent states are shown by solid lines and a dotted line is used for the charge-transfer (CT) states. The potential of the covalent states along the coordinate is shown for the subunit in the ground and excited electronic states. The potential for the CT states along the coordinate is shown for in the ground and excited states. The blue line in the plane along the coordinate corresponds to the CT state. The energy parameters of the CT states shown in the figure correspond to the calculated values for the complex (see text). In the plane along the coordinate the two lower arrows correspond to vertical transitions from the ground state to the CT state and to the covalent state . In the inset the region of diabatic curve crossing (region ) is given in more detail. The diabatic states and provided by an avoided crossing are shown. A vertical transition to the point provides excitation to the branch of state . The direct dissociation via trajectory corresponds to channel C1 (Fig. 1). Dissociation preceded by vibrational motion in the state corresponds to channel C2.
Cross section of the potential energy surface of the complex along the C–I coordinate. Solid line 1 corresponds to the ground state of the complex and solid line 2 corresponds to the excited state of complex where the methyl iodide is in a repulsive state. These profiles were built with the use of energy values calculated by Tadjeddine et al. in the representation for the states and of (Ref. 45). The dashed line 3 corresponds to the charge-transfer state. This potential was assumed to be similar to the potential of the ion which in turn was taken to be similar to the potential of the ground state of because of the nonbonding character of ionization in methyl iodide (Refs. 40 and 46). The gap between the minima of the CT state and the ground state of the complex corresponds to , as calculated in this work. The dotted line indicates the photon energy.
Velocity distribution profiles (reproduced from Fig. 2 of Ref. 16 with permission) obtained by DeBoer et al. for atoms arising from the photodissociation of clusters at . (A) Distribution of the velocity projection on the axis parallel to the polarization direction of photolysis light; (B) the same for the axis perpendicular to the polarization direction. (a) Projection of the crushed velocity map image obtained in our experiment on the photodissociation of clusters at the same wavelength [Fig. 1(d)] onto the vertical axis (parallel to the laser polarization direction); (b) projection of the same image on the horizontal axis (perpendicular to the laser polarization direction).
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