Product distribution quantum states

In summary the new field of surface aligned photoreactions has already generated some interesting data. As increasingly efficient trajectory calculations become available it should prove possible to obtain detailed insights into the dynamics of these reactions. However, better characterization of the surface layer and product internal quantum state distribution will be important in providing data with which to test the calculations. 

Rettner C T and Auerbach D J 1996 Quantum-state distributions for the HD product of the direct reaction of H(D)/Cu(111) with D(H) incident from the gas phase J. Chem. Phys. 104 2732... 

Gray and Wozny [101, 102] later disclosed the role of quantum interference in the vibrational predissociation of He Cl2(B, v, n = 0) and Ne Cl2(B, v, = 0) using three-dimensional wave packet calculations. Their results revealed that the high / tail for the VP product distribution of Ne Cl2(B, v ) was consistent with the final-state interactions during predissociation of the complex, while the node at in the He Cl2(B, v )Av = — 1 rotational distribution could only be accounted for through interference effects. They also implemented this model in calculations of the VP from the T-shaped He I C1(B, v = 3, n = 0) intermolecular level forming He+ I C1(B, v = 2) products [101]. The calculated I C1(B, v = 2,/) product state distribution remarkably resembles the distribution obtained by our group, open circles in Fig. 12(b). 

Since H-atom products from chemical reactions normally do not carry any internal energy excitation with its first excited state at 10.2 eV, which is out of reach for most chemical activations, the high-resolution translational energy distribution of the H-atom products directly reflects the quantum state distribution of its partner product. For example, in the photodissociation of H2O in a molecular beam condition,... 

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... 

Key topics covered in the review are the analysis of the wavepacket in the exit channel to yield product quantum state distributions, photofragmentation T matrix elements, state-to-state S matrices, and the real wavepacket method, which we have applied only to reactive scattering calculations. 

Figure 4.15 shows the Boltzmann distribution for several values of kT/E for a system where the states have evenly spaced energies. At low temperatures, most of the molecules can be found at the lowest energy states, with energy level equal to zero. When the temperature is increased, more and more molecules are promoted to higher energy states. When a molecule has several degrees of freedom, such as translations, rotations, and vibrations, each has its own quantum states and partition functions, and then the overall partition function is a product of all these separate partition functions ... 

The essential principle of coherent control in the continuum is to create a linear superposition of degenerate continuum eigenstates out of which the desired process (e.g., dissociation) occurs. If one can alter the coefficients a of the superposition at will, then the probabilities of processes, which derive from squares of amplitudes, will display an interference term whose magnitude depends upon the a,. Thus, varying the coefficients a, allows control over the product properties via quantum interference. This strategy forms the basis for coherent control scenarios in which multiple optical excitation routes are used to dissociate a molecule. It is important to emphasize that interference effects relevant for control over product distributions arise only from energetically degenerate states [7], a feature that is central to the discussion below. 

Figure 19. Comparison of the quantum (filled circles, long dashes) and the classical (solid lines) rotational product distributions of C>2(n = 0) following the dissociation of HO2 for four energies as indicated the precise energies of the corresponding quantum resonances are 0.1513, 0.2517, 0.3507, and 0.4471 eV, respectively. Also shown are the distributions obtained from PST (short dashes). All distributions are normalized so that the areas under the curves are equal. The arrows on the 7 axis indicate the highest accessible state at the respective energy and the vertical bars on the classical curves indicate7sACM, the highest populated state according to the SACM. (Reprinted, with permission of the American Institute of Physics, from Ref. 37.)...

With all of these new tools, it is no wonder that there has been an explosion of papers on photochemical dynamics, so much so that in this review we shall limit ourselves to those papers that have appeared over the last three years. Earlier reviews cover the work before this time, and the papers that are cited also give references to the earlier work. The papers that are covered are further limited to those that measure and discuss the detailed quantum state distribution of one or more of the photochemical fragments. Those papers that are limited to final product analysis are discussed only if the results bear directly upon the dynamics of the photochemical process. The review is organized so that molecules with similar chromo-phore groups are all discussed at the same time. This emphasizes the similarities and differences between these molecules. The discussion of the molecular systems begins after a brief discussion of some of the newer experimental techniques. In this review any earlier reviews that cover that molecule are cited along with the later papers on the subject. 

From the infrared emission, a non-Boltzmann vibrational distribution was observed in the HC1 product and by analysing the various relaxation processes, the absolute rates into each quantum state were investigated. Charters and Polanyi163 employed total pressures of 10-2 torr, with HC1 partial pressures of 10-4 torr, in order to avoid Boltzmannisation by V-V transfer. According to the equations of Section 3, is 9 at 400 °K, corresponding to a relaxation time of 3 x 10-2 sec for the process... 

The triplet energy of thianaphthene 1,1-dioxide was determined by two indirect methods. The first involved the use of several sensitizers of decreasing triplet energy. The results summarized in Table 1 indicate that triplet lies between 53 and 49 kcal mol-1. The second method is more precise and involves the use of thianaphthene 1,1-dioxide as a sensitizer to establish a photostationary state of the a—methylstilbenes. The composition of the photostationary state of a-methylstilbene has been determined as a function of the triplet energy level of the sensitizer. The results indicate a triplet energy for thianaphthene 1,1-dioxide of 50 1 kcal mol-1. Quantum yields of the photodimerization of thianaphthene 1,1-dioxide were determined in benzene as a function of concentration. Oisc is 0.18. The product distribution as a function of solvent polarity demonstrates the ratio of the head-to-head to head-to-tail dimer (HH/HT) increases with the polarity of the solvents. This is consistent with preferential solvatation of the head-to-head transitions state. 

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