Argon excited, reactions

The C8 reaction products in Table III illustrate that tert-C4H9+ reacts nonselectivity at both the primary and tertiary carbons in isobutylene. tert-C4H9+ is formed by Reaction 1 which is estimated to be 10-20 kcal./mole exothermic in the gas phase. It is postulated that vibrationally excited tert-C4H9+ is formed in the gas phase and exhibits this by non-selective reactivity in the liquid phase. Two independent sets of experiments support this. When tert-C4H9+ is de-excited in the gas phase by collisions with added argon, its reaction selectivity towards liquid isobutylene increases. When Reaction 1 takes place in the liquid phase, nonexcited ter -C4H9+ is formed which exhibits considerable reaction selectivity towards 2-butene. 

In the Gas Phase. Schmitt et al. (32, 33) found that ArH + and N02 couple in the gas phase to give the a complex (ArHN02) +. The ArH + was produced by ionization of ArH with photons emitted from pulse-radiation excited argon atoms. Reactions were carried out in a flow system within the source of a quadrupole mass spectrometer. In contrast, reactions of the corresponding ArH with N02+ were found not to go directly to (ArHN02) + but to lead either to ArH + and N02 by fast electron transfer or to (ArHO) + and NO by oxygen-atom transfer. From these results, Schmitt et al. (32, 33) concluded that aromatic radical cations are a plausible intermediate in the mechanism for aromatic nitration. ... 

Herman and Cermak estimated the mean path of the excited reactants in their experiments to be 0.25 cm and, combining this with an estimate of the ratio of excitation to ionization cross sections for argon, calculated reaction cross sections of 1.5 x 10 cm, 2 x 10 cm, and 5 X 10" cm, respectively, for the formation of ArNa, ArK", and ArCs" ... 

In most cases, ion activation in the reaction region or fragmentation zone is applied to increase the internal energy of the ions transmitted from the ion source. The most common means of ion activation in tandem mass spectrometry is collision-induced dissociation. CID uses gas-phase collisions between the ion and neutral target gas (such as helium, nitrogen or argon) to cause internal excitation of the ion and subsequent dissociation... 

The samples were collected from the cathodes 2.5 cm away from the current collector tab, washed in pure dimethyl carbonate (DMC), and soaked in DMC for 30 minutes after removal from Li-ion cells inside an argon-filled glove box. This procedure removed electrolyte salt from the electrode to prevent its reaction with air and moisture. An integrated Raman microscope system Labram made by ISA Groupe Horiba was used to analyze and map the cathode surface structure and composition. The excitation source was an internal He-Ne (632 nm) 10 mW laser. The power of the laser beam was adjusted to 0.1 mW with neutral filters of various optical densities. The size of the laser beam at the sample was 1.2 pm. 

We can illustrate the application of PAC to a simple photochemical reaction. Acetone is readily excited to its singlet excited state which rapidly undergoes efficient intersystem crossing to its triplet state. The triplet state decays in solution primarily by radiationless decay. The PAC experimental waveforms obtained from the photoexcitation of acetone in air and argon-saturated cyclohexane are shown in Fig. 1. In addition, the waveform obtained from the calibration compound 2-hydroxybenzophenone is also shown. 

The photochemical reaction was initiated with a UV source, and an argon-ion laser was used as the fluorescence excitation source (2 = 457.9 nm). A... 

The production of NOz, with NO as a possible precursor to NOz, has been observed when synthetic air or 02/N2 mixtures are photolyzed using a deuterium lamp, an argon flash lamp, or a 185-nm mercury line (Zipf and Prasad, 1998a). They proposed that this occurs from the reaction of electronically excited 02(B%) with N2, or photodissociation of 02 N2 dimer, and that the rate of NOx production from this process could be comparable to that from reaction (13b) (Zipf and Prasad, 1998a Prasad, 1998). If this proves to be the case, there must be some unidentified NOx sinks to be consistent with the measured NOx concentrations in the upper atmosphere. 

However, the foregoing observations cannot definitely be ascribed to triplet CH2 for the following reasons. Dilution of the reaction mixture with argon while maintaining constant total pressure leads to decreased deactivation efficiency, as pointed out by Frey, and therefore the loss of stereospecificity may result from geometric isomerization of the initial excited adducts rather than from a different mechanism of reaction of triplet methylene. 

The effect of added 02 can be explained by high deactivation efficiency of 02 toward the excited adducts and does not necessarily indicate reaction of 02 with triplet methylene or triplet intermediates. In fact, the overall results for added argon and added 02 can be explained by deactivation efficiencies in the ratio Ar butene-2 02 = 1 102-5 104-5. The results of both Frey and Anet42 and Anet et al.2 are from this point of view quite comparable with each other. We see that as we... 

Clyne, Thrush, and Wayne107 reexamined the chemiluminescence from the nitric oxide-ozone reaction and found its spectrum to be similar to that of the thermal emission of N02 at 1200°K. They concluded that the spectra represented transitions from similar low-lying vibration levels of the same excited electronic state of NOa to the ground state. By measuring the decay in chemiluminescence down a flow tube, they obtained the value of the rate constant between 216 and 322°K. The partial pressures of ozone and nitric oxide were 5 x 10-3 and 2 x 10 2 torr, respectively, in an argon carrier at a total pressure of 2 torr. In the presence of excess nitric oxide, they assumed the logarithmic disappearance of ozone proportional to [NO], so that... 

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