Photodissociation dynamics of nitrobenzene and o-nitrotoluene

Abstract

Photodissociation of nitrobenzene at 193, 248, and 266 nm and o-nitrotoluene at 193 and 248 nm was investigated separately using multimass ion imaging techniques. Fragments corresponding to NO and NO(2) elimination from both nitrobenzene and o-nitrotoluene were observed. The translational energy distributions for the NO elimination channel show bimodal distributions, indicating two dissociation mechanisms involved in the dissociation process. The branching ratios between NO and NO(2) elimination channels were determined to be NONO(2)=0.32+/-0.12 (193 nm), 0.26+/-0.12 (248 nm), and 0.4+/-0.12(266 nm) for nitrobenzene and 0.42+/-0.12(193 nm) and 0.3+/-0.12 (248 nm) for o-nitrotoluene. Additional dissociation channels, O atom elimination from nitrobenzene, and OH elimination from o-nitrotoluene, were observed. New dissociation mechanisms were proposed, and the results are compared with potential energy surfaces obtained from ab initio calculations. Observed absorption bands of photodissociation are assigned by the assistance of the ab initio calculations for the relative energies of the triplet excited states and the vertical excitation energies of the singlet and triplet excited states of nitrobenzene and o-nitrotoluene. Finally, the dissociation rates and lifetimes of photodissociation of nitrobenzene and o-nitrotoluene were predicted and compared to experimental results.

How important is roaming in the photodegradation of nitrobenzene?

“…For the fast molecule, however, the photoisomerization is mediated by the formation of an oxaziridine ring on the triplet states, as previously suggested by Lin et al and by Zewail and coworkers and documented for other nitroaromatic systems, 13,[15][16][17] while for the slow product the photoisomerization is suggested to occur on the ground state according to a roaming mechanism.…”

“…11,12 The photodegradation of nitrobenzene to form NO has been proven to occur via two mechanisms. 13,14 Employing multimass ion imaging techniques on nitrobenzene vapor, Lin et al have determined a bimodal distribution of the translational energy of the NO molecules, which points to the presence of two different paths leading to NO photorelease. 13 The bimodal distribution was observed exciting the system at 248 and 193 nm (5.00 and 6.42 eV), while employing a 266 nm (4.66 eV) wavelength only the slow component was observed.…”

Investigation on VOC Emissions from Automobile Sources by Means of Online Mass Spectrometry

“…The strategy for preventing refueling emissions in the USA is to employ an onboard-refueling vapor recovery (ORVR) system, which traps the vapor displaced by the liquid fuel entering into the tank, by using a carbon canister installed in the car. Unlike the USA, in Europe, the refueling emissions are vacuumed by a stage II system installed on a gasoline dispenser [83]. These two are the commonly used techniques, and often countries wishing to control refueling emissions choose one of them after considering their merits and disadvantages.…”

Initial mechanisms for the dissociation of carbon from electronically-excited nitrotoluene molecules

“…Typical photodissociation products that have been reported previously include: C n H m , NO 2 , NO, O, OH, CO, etc. 7 As part of an investigation to develop a better understanding of potential approaches for the detection of explosive molecules, we recently reported on the experimental observation of neutral carbon during the photodissociation of various nitrotoluene molecules. 15 Using a timeresolved fluorescence technique, we observed emission from nitric oxide (NO) and neutral carbon (C) when we excited trace amounts of 2-NT, 4-NT, 2,4-DNT, 3,4-DNT, and 2,6-DNT in nitrogen and air.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Besides developing a better understanding of the combustion and decomposition properties, developing a better understanding of the photodissociation processes of these molecules may also lead to the development of laser-based detection methods of explosives. Typical photodissociation products that have been reported previously include: C n H m , NO 2 , NO, O, OH, CO, etc.…”