Dissociation energy and photochemistry of NO[sub 3]
- Lawrence Berkeley Lab., CA (United States)
The photodissociation of NO[sub 3] was studied using the method of molecular beam photofragmentation translational spectroscopy. The existence of two photodissociation channels was confirmed under collision-free conditions. At excitation energies below D[sub 0](O-NO[sub 2]) for internally cold NO[sub 3], the authors observe a large quantum yield (0.70 [+-] 0.10 at 588 nm) for a concerted three-center rearrangement resulting in NO([sup 2][Pi]) + O[sub 2]([sup 3][Sigma][sub g][sup [minus]],[sup 1][Delta]). The quantum yield for the NO + O[sub 2] channel decreased sharply at wavelengths shorter than 587 nm, falling to <0.01 at 583 nm, while the NO[sub 2] + O([sup 3]P) quantum yield increased to >0.99. On the basis of this wavelength dependence and the product translational energy distributions, the authors conclude that the wavelength threshold for NO[sub 3](0,0,0,0) [yields] NO[sub 2](0,0,0) + O([sup 3]P[sub 2]) is 587 [+-] 3 nm, i.e. D[sub 0](O-NO[sub 2]) = 48.69 [+-] 0.25 kcal/mol. From the enthalpies of formation of O([sup 3]P[sub 2]) and NO[sub 2]([sup 2]A[sub 1]), they calculate [Delta]H[sub f][degrees](NO[sub 3]) = 18.87 [+-] 0.33 kcal/mol at 0 K and [Delta]H[sub f][degrees](NO[sub 3]) = 17.62 [+-] 0.33 kcal/mol at 298 K. This is 2.23 kcal/mol higher than the most recent thermochemical value but is consistent with a value calculated indirectly using the most recent values for the electron affinity (EA) of NO[sub 3] and [Delta]H[sub f][degrees](NO[sub 3][sup [minus]]). From the wavelength dependence and translational energy distributions for NO[sub 3] [yields] NO + O[sub 2], the potential energy barrier for NO[sub 3]([sup 2]A[prime][sub 2]) [yields] NO([sup 2][Pi]) + O[sub 2]([sup 2][Sigma][sub g][sup [minus]]) was found to be 47.3 [+-] 0.8 kcal/mol. 53 refs., 15 figs., 2 tabs.
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6234179
- Journal Information:
- Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 97:10; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201 -- Chemical & Physicochemical Properties
400500* -- Photochemistry
BEAMS
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
DISSOCIATION ENERGY
ENERGY
ENTHALPY
MOLECULAR BEAMS
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMISTRY
PHYSICAL PROPERTIES
PYROLYSIS
RADICALS
SPECTROSCOPY
THERMOCHEMICAL PROCESSES
THERMODYNAMIC PROPERTIES
THERMODYNAMICS