Excited Ozone

Vibrationally Excited Ozone.—Ozone can be promoted to its (001) vibrational level as a result of chance coincidences between lines in the (001,000) fundamental band of Os and lines from a COa laser, the strongest overlap being with the P(30) line in the 9.6 /um band. This has been the basis for a number of experimental studies of the enhanced reactions of Osf with NO, 02( ), and SO.  

The reaction between NO and Os is especially interesting since it can proceed by two distinct routes -  

The enhancement of reactions (79a) and (79b) when Os is vibrationally excited was first observed by Gordon and Lin using a repetitively pulsed COi laser. Since that time they have extended their measurements. With the low Os concentrations and high laser powers in their latest experiments, Gordon and Lin believe that equilibration of the initial vibrational excitation is unimportant so 

The reactions between NO and vibrationally excited O3 have also been studied by Braun and his colleagues, but under somewhat different conditions from those in Gordon and Lin s experiments. In their experiments, the ozone is excited by the square wave modulated output from a cw CO2 laser. Although they also observed enhanced reaction, their conclusions appear to differ in detail from those of Gordon and Lin. They believe that under their conditions, rapid V-V equilibra tion among the O3 modes precedes reaction. Their results can then either be interpreted on the basis that all these modes are equally active, in which case at 300 K the ratio of the enhanced rate constant for (79a) to the thermal rate constant is 4.2, or by assuming that only the v, and V3 stretching modes effectively promote reaction when the ratio of rate constants becomes 16.4. Kurylo era/. prefer the former of these two explanations. 

Although the reactions of Osf with NO have received most attention, results have also been reported for the vibrational enhancement of the reactions 

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Zipf, E. C., and S. S. Prasad, Experimental Evidence That Excited Ozone Is a Source of Nitrous Oxide, Geophys. Res. Lett, 25, 4333-4336 (1998b). 

Effect of 03. Adding ozone in dioxygen or air is a very efficient means of enhancing the photocatalytic rates of the removal and, above all, the mineralization of organic pollutants both in air and in water, even if the wavelengths are intentionally selected so as not to excite ozone (39 41). This substantial effect is attributed to the difference in electron affinity between 03 (2.1 eV) and 02 (0.44 eV). Consequently, in the presence of ozone, the electrons photopromoted to the Ti02 conduction band can be captured more easily, either directly ... 

A chemically based, mass-independent fractionation process was first observed during ozone formation through the gas-phase recombination reaction (Thiemens Heidenreich 1983) O + O2 + M - O3 + M. The product ozone possesses equally enriched heavy-oxygen isotopes I7 IS0. by approximately lOO /oo with respect to the initial oxygen, with a slope value of unity in a three-isotope oxygen plot. This discovery led to the conclusion that a symmetry-dependent reaction can produce meteoritic isotopic anomalies (Thiemens 1999, 2006). Recently, theoretical calculations of Gao Marcus (2001) established the major role of symmetry in isotopolog-specific stabilization of vibrationally excited ozone molecules that give rise to the mass-independent compositions. 

Another interesting result obtained in experiments on these ratios of rate constants is the lack of the dependence of the ratio on the nature of the gas collisionally deactivating the vibrationally excited ozone isotopomer [46]. Different mechanisms have been postulated for the collisional deactivation, including the energy transfer mechanism used here and most commonly used elsewhere, and a chaperon mechanism in which the third-body collision partner forms collision complex with the Q or with the Q2 prior to the recombination step. Recently the chaperon mechanism was revisited for ozone formation, analyzing pressure and temperature dependent data on the recombination rate [47]. Since the ratios of rate... 

As an example of a unimolecular reaction, consider the elementary process in which an energetically excited ozone molecule (symbolized by O3) spontaneously decomposes. 

Adler-Golden, S.M. Franck-Condon analysis of thermal and vibrational excitation effects on the ozone Hartley continuum. J. Quant. Spectrosc. Radiat. Transf. 30, 175-185 (1983) Adler-Golden, S.M., Schweitzer, E.L., Steinfeld, J.I. Ultraviolet continuum spectroscopy of vibrationally excited ozone. J. Chem. Phys. 76, 2201-2209 (1982)... 

The sample is burned in oxygen at 1000°C. Nitrogen oxide, NO, is formed and transformed into NO2 by ozone, the NO2 thus formed being in an excited state NO. The return to the normal state of the molecule is accompanied by the emission of photons which are detected by photometry. This type of apparatus is very common today and is capable of reaching detectable limits of about 0.5 ppm. 

Quack M and Sutcliffe E 1983 Quantum interference in the IR-multiphoton excitation of small asymmetric-top molecules ozone Chem. Phys. Lett. 99 167-72... 

A recent study of the vibrational-to-vibrational (V-V) energy transfer between highly-excited oxygen molecules and ozone combines laser-flash photolysis and chemical activation with detection by time-resolved LIF [ ]. Partial laser-flash photolysis at 532 mn of pure ozone in the Chappuis band produces translationally-... 

Nickel Carbonyl The extremely toxic gas nickel carbonyl can be detected at 0.01 ppb by measuring its chemiluminescent reaction with ozone in the presence of carbon monoxide. The reaction produces excited nickel(II) oxide by a chain process which generates many photons from each pollutant molecule to permit high sensitivity (315). 

Ozone can be destroyed thermally, by electron impact, by reaction with oxygen atoms, and by reaction with electronically and vibrationaHy excited oxygen molecules (90). Rate constants for these reactions are given ia References 11 and 93. Processes involving ions such as 0/, 0/, 0 , 0 , and 0/ are of minor importance. The reaction O3 + 0( P) — 2 O2, is exothermic and can contribute significantly to heat evolution. Efftcientiy cooled ozone generators with typical short residence times (seconds) can operate near ambient temperature where thermal decomposition is small. 

The mechanism for ozone generation is the excitation and acceleration of stray... 

D) is an electronically excited oxygen atom. It can decay back to a ground state oxygen atom ( P) (which will regenerate an ozone molecule), or else it can react with water to produce two OH radicals ... 

The Brueckner-reference method discussed in Section 5.2 and the cc-pvqz basis set without g functions were applied to the vertical ionization energies of ozone [27]. Errors in the results of Table IV lie between 0.07 and 0.17 eV pole strengths (P) displayed beside the ionization energies are approximately equal to 0.9. Examination of cluster amplitudes amd elements of U vectors for each ionization energy reveals the reasons for the success of the present calculations. The cluster operator amplitude for the double excitation to 2bj from la is approximately 0.19. For each final state, the most important operator pertains to an occupied spin-orbital in the reference determinant, but there are significant coefficients for 2h-p operators. For the A2 case, a balanced description of ground state correlation requires inclusion of a 2p-h operator as well. The 2bi orbital s creation or annihilation operator is present in each of the 2h-p and 2p-h operators listed in Table IV. Pole strengths are approximately equal to the square of the principal h operator coefiScient and contributions by other h operators are relatively small. 

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