Anisotropy parameter photodissociation

From the translational energy distributions obtained above, the quantum state distributions and the quantum state-specific anisotropy parameters can be determined. In a molecular photodissociation process, the photodissociation product detected at an angle in the center-of-mass... 

The bimodal velocity distribution of the 0(3Pj) fragments produced via the triplet channel in the UV photodissociation of ozone has also been observed by Syage41,43>46 and Stranges et al.AA at photolysis wavelengths of 226 and 193 nm, respectively. Both authors measured anisotropy parameters for the fast and slow product pathways separately. 

Fig. 17. H-atom product channel translational energy distributions of the ethyl photodissociation, with the 245-nm photolysis radiation polarization (a) parallel to the TOF axis (b) at magic angle and (c) perpendicular to the TOF axis, and (d) anisotropy parameter /3(Et). In (b), the de-convoluted fast component, P[(i T), and slow-component, Pii(E ), are plotted in dashed and dotted lines, respectively. (From Amaral et al,39)...

The increases that are observed in the anisotropy parameter with increasing wavelength are thought to be due to the non-negligible lifetime of the iBj state, which proves that predissociation must be occurring in the photolysis. There is no indication in the absorption spectra that this is the case, which illustrates how photodissociation dynamics can reveal new details about the upper electronic states of the molecule. 

The rapid predissociation of the excited 082( 52) formed in the 193-nm excitation is believed to be the mechanism for the formation of CS + S. The Doppler spectroscopic experiment shows anisotropy in dissociation and provides a lifetime of 1-2ps for the excited 082( 52) state [94]. The TOF study of Frey and Felder [83] indicates that the 193-nm photodissociation C82 is anisotropic and that the parameters for processes 11 and 12 are different. 

Figure 2.12 Controlling the impact parameter in the Br+l2 reaction. Here the anisotropy of the van der Waals potential is such that the preferred configuration is H—Br l—I. Upon photodissociation of HBrthe H atom moves away rapidly while the Br atom approaches I2 slowly (why slowly ). The Brl2 species vibrates for a while, see Figure 8.5, before it dissociates to BrI and I. The bound and repulsive potentiais involved in the initial photodissociation of the H—X bond are also shown [adapted from Wittig eta/. (1988)].

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