ordinary cw spectra. We attribute this to their direct dependence on the T z j according to eq 1 .We expect that as 2D-ESE techniques are further developed, they will provide a very useful method to enable detailed studies of structure and dynamics in oriented media.The use of absorption and emission spectroscopy of photodissociating molecules is discussed as a means of probing details of dissociation dynamics in extremely short-lived transient species. The study of photodissociation processes has special advantages which derive from the special ability to create well-defined initial conditions and from the simplicity of interpretation of experimental results. Casting the absorption and emission processes in a time-dependent formalism developed by Heller and co-workers enables intuitive connections to be made between spectroscopic features and the underlying dynamics. The absorption spectrum of photodissociating molecules primarily contains information about very short-time dynamics, whereas the emission spectrum reveals more details and encompasses intermediate times as well. Information about both the excited-state and the ground-state potential surfaces is contained in the emission spectrum. Intensities of fundamentals, overtones, and combinations can be used to infer properties of the upper-state surface (such as forces and their gradients). The observed energies and band contours of the same features yield characteristics of the ground-state surface. Experimental results on methyl iodide and ozone are used to illustrate how emission spectra can be used to study reaction dynamics.

No abstract

The formation of OH in the shock wave induced combustion of H2 and O2 has been measured by oscillographically recording the absorption of ultraviolet OH line radiation. The main features of the reaction course are: (1) an induction period whose length, ti, varies inversely with [O2], (2) an increase in the product [O2] ti as ti becomes short compared to the vibrational relaxation time of O2, and (3) at the end of the induction period, a sigmoid rise of [OH] to a maximum, followed by a slow decrease. ti has been studied over the ranges: 1100°≤T≤2600°K, 1.3×10—5≤[O2]≤8.0×10—4 mole/1, 0.25≤[H2]/[O2]≤5., 0.004≤[O2]/[Ar]≤0.20, and 5≤ti≤500 μsec. Agreement between incident and reflected shock experiments has been demonstrated. According to the branching chain mechanism known from explosion limit studies, ti is governed by the rate of H+O2→ lim k1OH+O according to: 2 k1[O2]ti=2.303 n, where n is the number of decades by which [OH] increases between initiation and the end of the induction period. The values of [O2]ti, which is nearly proportional to 1/k1, are summarized by: log10([O2]ti) (mole 1—1 sec)= —10.647+(3966±625)/T. The value k1=1.4×109 deduced at 1650°K from this work is combined with data near 800°K to give: k1=3×1011 exp(—17.5±3. kcal/RT) (mole/1)—1 sec.—1. The relation of these results to detonation experiments is discussed.

No abstract

Resonance Raman spectroscopy as a probe of the early stages in the dissociation dynamics of polyatomic molecules has become a valuable complement to photofragmentation studies. While these spontaneous Raman experiments are obtained in the frequency domain, they often reflect evolution of the molecule during the first few femtoseconds of bond breaking. Coupled with progress in classical and quantum calculations of large-amplitude motion, unique insights have become available for a number of small polyatomic molecules. The development of this field to date is reviewed.