Rotational Energy Disposal

Rotational Energy DtsposaL—Among the flurry of papers which have been dedicated towards modelling the dynamics of photodissociation, very few have been directed towards the problem of rotational energy disposal (though one is promised The classical example of rotational excitation in the photodissociation of H2O, 

The observed distribution over rotational levels has been treated in terms of statistical modds, though it is doubtful whether a statistical apjn oach is justified for direct photodissociation or predissociation via intersecting states. A simple impulsive model has been used to explain the Maxwellian rotational distributions in CN(A) produced in the photodissodation of cyanogen and dicyanoacetylene.  

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For the reactions H, D + Br2 there has been less experimental confirmation about the product vibrational and rotational energy disposal. Fast-flow infrared chemiluminescence measurements [241] yield a product vibrational distribution that differs from earlier measurements [228]. A recent molecular beam study [235] for D + Br2, at a lower collisional energy (5.3 kJ mole-1) than the earlier beams studies ( 42 kJ mole-1), gives CFX> = 0.40, which agrees more closely with the 300 K chemiluminescence value, CFX> = 0.41 [228], than does the higher energy beams value [111] of (FT) = 0.31. 

Many semi-classical and quantum mechanical calculations have been performed on the F + H2 reaction, mainly being restricted to one dimension [520, 521, 602]. The prediction of features due to quantum-mechanical interferences (resonances) dominates many of the calculations. In one semi-classical study [522], it was predicted that the rate coefficient for the reaction F (2P1/2) + H2 is about an order of magnitude smaller than that for F(2P3/2) 4- H2, which lends support to the conclusion [508] that the experimental studies relate solely to the reaction of ground state fluorine atoms. Information theory has been applied to many aspects of the reaction including the rotational energy disposal and branching ratios for F + HD [523, 524] and has been used for transformation of one-dimensional quantum results to three dimensions [150]. Linear surprisal plots occur for F 4- H2(i> = 0), as noted before, but non-linear surprisal plots are noted in calculations for F + H2 (v < 2) [524],... 

An estimation of the spin-orbit branching ratio in the ground ( E) state of the CH3S product, and of the rotational energy disposal in the vibrationless products, both as a function of excitation wavelength... 

The translational spectra supplement data obtained from angular distributions alone and provide information on the internal and translational energies of the photofiragmeats and their initial electronic states, though it may be difBcult (or impossible) to separate the vibrational and rotational energy disposal when the rotational distributions are broad and/or the densities of states are high. 

Studies of vibrational (and rotational) energy disposal in the vacuum u.v. photodissociation of cyanogen, hydrogen cyanide, and the cyanogen halides, were reported by Mele and Okabe and the estimated vibrational distributions in the dissociations... 

CL and LIE spectra are the ideal sources of information on vibrational, and to a lesser extent of rotational, energy disposal. Extracting reliable population analyses from the generally congested spectra is however more demanding on one s... 

The vibrational energy disposal has been studied by the infrared chemiluminescence technique for a large number of polyatomic molecules (see Table 2.6) however, the interpretations are not as advanced as for the F + HR systems. The rotational energy disposal is somewhat less completely studied, but such data can be expected in the near future. With certain exceptions, the energy disposal generally resembles that of the H + Xa reactions with small , moderate , and nonlinear vibrational surprisals and failure of the HCl or KF product distribution to extend to the thcriiiO-chemical limit. The reactions with NOCl and the sulfur chlorides have been studied in greatest detail and the discussion will be focused on these reactions. 

CS vibrational energy of 2 kcal mole" (retained from the O + CS2 formation reaction) was used to calculate < >. No experimental data have been obtained for the rotational energy disposal to CO. 

Subsequent experimental measurement of the HF and DF rotational distributions gave quantitative agreementwith the prediction. Both the information-theoretic and kinematic-potential surface interpretations lead to the same conclusion namely, the difference in rotational energy disposal... 

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