Molecular function photodissociation

The earliest molecular beam infrared experiments on Van der Waals complexes used photodissociation spectroscopy a molecular beam is irradiated witli a tunable infrared laser and tire molecular beam intensity is measured as a function of... 

In polymerization with the compounds having a photodissociable DC group as photoiniferters, the polymerization can be performed at low temperature, such as room temperature, in contrast with thermal iniferters. Moreover, we can readily prepare many kinds of DC derivatives with various structures, indicating that the functionalization and molecular structure design are easy [156]. 

Photodissociation involves electronic transitions initiated by the absorption of light. The key molecular property that mediates the interaction with light is the transition dipole moment. The electronic transition dipole moment between the jth and kth electronic state is defined by the integral over the electronic degrees of freedom for the operator where the dipole moment is sandwiched between the two electronic wave functions given by... 

In order to evaluate partial photodissociation cross sections (vibrational and rotational product distributions) i.e. ABC + hv A + BC n,K) the wave function can be projected onto the different rovibrational eigenstates of the molecular fragment BC at fixed distance R between the two fragments. The chosen R should be on the asymptote of the potential energy surface where the two fragments do not interact. Balint-Kurti et at [87] have shown that the partial cross section is given by... 

Details of the photoexcitation and dissociation of seeded supersonic molecular beams of I2 by 514.5 nm radiation from a CW Ar laser have been provided by Bernstein and co-workers.A number of measurements were made, including LIF, I2 beam attenuation, and I2 TOF distributions as functions of carrier-gas pressure and nozzle temperature. A value for the direct photodissociation cross-section for I2 was determined to be (2.4 0.5) x 10 cm from measurements of the laser-induced beam loss. Use of additional spectroscopic information enabled calculation of the fraction of molecules excited on the basis of a simple model, and comparisons of the degree of excitation for different beam conditions and beam/laser geometries were made. 

The development of the picosecond-jet technique is presented. The applications of the technique to the studies of coherence (quantum beats), photodissociation, isomerization and partial solvation of molecules in supersonic-jet beams are detailed with emphasis on the role of intramolecular energy redistribution. Experimental evidence for intramolecular threshold effect for rates as a function of excess molecular energy is given and explained using simple theory for the redistribution of energy among certain modes. Comparison with R.R.K.M. calculation is also made to assess the nature of the statistical behaviour of the energy redistribution. 

Figure 4-34- Contribution of each spectral region to the photodissociation of molecular oxygen as a function of altitude.

Figure 4.37 shows the relative contribution of each band to the ozone photolysis frequency as a function of altitude. It should be noted that the value of the ozone photodissociation coefficient depends critically on the absorption by ozone itself, introducing a nonlinear coupling as a function of altitude. The calculation of Jo3 must include the effects of molecular scattering and albedo (see Figure 4.38). 

When a superexcited molecular state of energy E is created by either 1-photon absorption of uq or 3-photon absorption of uq, molecular photofragmentation can occur into either of two qualitatively distinct channels, photodissociation (D) and photoionization (I). The excitation probabilities, as a function of E for the D and I channels, are... 

Fig. 19. Radial distribution functions f(r) and f(r) derived from the molecular scattering curves for gaseous CHJ2 at different delay times between the photodissociating fs laser pulse (at A = 310 nm) and the ps electron pulse (pulse-width 15 ps). The corresponding theoretical f(r) curve for CH2I2 is superimposed on the — 20-ps data set. The changes observed are at r = ca. 2.0 and 3.5 A corresponding to the C—I and I—I internuclear spacings, respectively [reproduced with permission from (96), p. 161],...

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