NO2, excited

Since the photoreactions occur in a constant ratio, that is, L/R 2.5, an LMCTeEjCo) No2 excited state is eventually populated regardless of whether the... 

The fluorescence from NO2 excited by the 4416 and 4880 A lines is used for measuring NO2 concentrations in air in the parts per billion range (388). 

A more recent work by Paech ct al. (789) on the collision-free lifetimes of NO2 excited by a tunable laser near 4880 and 5145 A states that although only a single level is excited, three different lifetimes of fluorescence, 3, 28, and 75 /isec, have been observed. The results lead them to conclude that the initially formed B, state crosses over rapidly to another state, Bi, with higher level density. The Bj state can have two different lifetimes (28 and 75 ftscc), depending on the extent of interaction with the ground state. The short life observed, 3 ftscc, is determined primarily by the rate of internal conversion from the B, to 82 state. The results of some reported collision-free fluorescence lifetimes are given in Table VI-6 . 

Fig. 1.56 LIF spectrum of NO2 excited at k = 590.8 nm. The vibrational bands terminating on ground-state vibrational levels (ui, U2, 3) marked with an asterisk are forbidden by symmetry selection rules but are made allowable by an admixture of a perturbing level with other symmetry to the excited-state wave function [182]...

Fig. 4.6 Section of the spectrum of NO2 excited at Aex = 488 nm in a collimated NO2 beam with a collimation ratio of sine = 1/80 (a) total fluorescence monitored and (b) filtered excitation spectrum, where instead of the total fluorescence only the fluorescence band at X = 535.6 nm for the lower vibrational level (0,10) was monitored by PM2 behind a monochromator [393]...

Fiq.l0.5a-c. Reduction of the complexity of the NO2 excitation spectrum by internal cooling in a supersonic beam, (a) Conventional room temperature sample of pure NO at 0.04 torr, (b) supersonic beam of pure NO , (c) supersonic beam of S% NO in Ar. The excitation source was a cw dye laser with 0.5 A bandwidth [10.13]... 

Figure 1.5. Stern-Volmer plots for the quenching of fluorescence from NO2 excited at 436 nm. [Adapted, with permission, from L. F. Keyser et al.,J. Chem. Phys., 54, 355 (1977).]...

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. 

Detailed analyses of the above experiments suggest that the apparent steps in k E) may not arise from quantized transition state energy levels [110.111]. Transition state models used to interpret the ketene and acetaldehyde dissociation experiments are not consistent with the results of high-level ab initio calculations [110.111]. The steps observed for NO2 dissociation may originate from the opening of electronically excited dissociation chaimels [107.108]. It is also of interest that RRKM-like steps in k E) are not found from detailed quantum dynamical calculations of unimolecular dissociation [91.101.102.112]. More studies are needed of unimolecular reactions near tln-eshold to detennine whether tiiere are actual quantized transition states and steps in k E) and, if not, what is the origin of the apparent steps in the above measurements of k E). 

Figure B2.3.15. Laser fluorescence excitation spectrum of the A S -X ff (1,3) band for the OH product, in the V = 3 vibrational level, from tire H + NO2 reaction [44]- (By pemrission from AIP.)...

Chou J Z and Fiynn G W 1990 Energy dependence of the reiaxation of highiy excited NO2 donors under singie coiiision conditions vibrationai and rotationai state dependence and transiationai recoii of CO2 quencher moiecuies J. Chem. Rhys. 93 6099-101... 

NO2 refers to the excited nitrogen oxide molecule. These molecules can decay by emission of light of wavelengths longer than 600 nm.- ... 

The nitration reagents (NO2 Y) for electrophilic aromatic nitration span a wide range and contain anions Y such as nitric acid (Y = OH-), acetyl nitrate (Y = OAc-), dinitrogen pentoxide (Y = NO3-), nitryl chloride (Y = Cl-), TV-nitropyridinium (Y = pyridine) and tetranitromethane [Y = C(N02)3-]. All reagents contain electron-deficient species which can serve as effective electron acceptors and form electron donor-acceptor (EDA) complexes with electron-rich donors including aromatic hydrocarbons107 (ArH, equation 86). Excitation of the EDA complexes by irradiation of the charge-transfer (CT) absorption band results in full electron transfer (equation 87) to form radical ion... 

The primary photochemical reaction for nitromethane in the gas phase is well supported by experiments to be the dissociation of the C—N bond (equation 98). The picosecond laser-induced fluorescence technique has shown that the ground state NO2 radical is formed in <5 ps with a quantum yield of 0.7 in 264-nm photolysis of nitromethane at low pressure120. The quantum yield of NO2 varies little with wavelength, but the small yields of the excited state NO2 radical increase significantly at 238 nm. In a crossed laser-molecular beam study of nitromethane, it was found that excitation of nitromethane at 266 nm did not yield dissociation products under collision-free conditions121. 

CgH (n = 6, 7, 8). A novel collision-induced isomerization of CgH7 (10a), which has a sttained allenic bond, to (lOyS) has been reported to occur upon SIFT injection of (10a) at elevated kinetic energies (KE) and collision with helium. In contrast, radical anions (9) and (11) undergo electron detachment upon collisional excitation with helium. Bimolecular reactions of the ions with NO, NO2, SO2, COS, CS2, and O2 have been examined. The remarkable formation of CN on reaction of (11) with NO has been attributed to cycloaddition of NO to the triple bond followed by eliminative rearrangement. 

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