Post-irradiation Temperature-programmed Desorption Research Articles

Formamidinium Halide Perovskite and Carbon Nitride Thin Films Enhance Photoreactivity under Visible Light Excitation.

Photochemical and photocatalytic activity of adsorbates on surfaces is strongly dependent on the nature of a given substrate and its resonant absorption of the (visible) light excitation. An observation is reported here of the visible light photochemical response of formamidinium lead bromide (FAPbBr3) halide perovskite and carbon nitride (CN) thin-film materials (deposited on a SiO2/Si(100) substrate), both of which are known for their photovoltaic and photocatalytic properties. The goal of this study was to investigate the role of the substrate in the photochemical reactivity of an identical probe molecule, ethyl chloride (EC), when excited by pulsed 532 nm laser under ultrahigh vacuum (UHV) conditions. Postirradiation temperature-programmed desorption (TPD) measurements have indicated that the C–Cl bond dissociates following the visible light excitation to form surface-bound fragments that react upon surface heating to form primarily ethane and butane. Temperature-dependent photoluminescence (PL) spectra of the FAPbBr3 films were recorded and decay lifetimes were measured, revealing a correlation between length of PL decay and the photoreactivity yield. We conclude that the FAPbBr3 material with its absorption spectrum in resonance with visible light excitation (532 nm) and longer PL lifetime leads to three times faster (larger cross-section) photoproduct formation compared with that on the CN substrate. These results contrast the behavior under ambient conditions where the CN materials are photochemically superior due, primarily, to their stability within humid environments.

Electron-Stimulated Formation and Release of Molecular Hydrogen and Oxygen from Boehmite Nanoplatelet Films

The production and release of H2 and O2 during and after electron (100–1000 eV) irradiation of boehmite nanoplatelet films was studied. H2 and O2 produced during irradiation likely correspond to electron-induced dissociation of the hydroxyls primarily in the terminal surface layers of the boehmite followed by the H· + H· → H2(g) and O + O → O2(g) combinative desorption reactions as well as the abstraction reactions H· + >OH– → H2(g) + >O·̅. Postirradiation temperature-programmed desorption shows a temperature-dependent release of H2 but no additional release of O2. This process likely involves diffusion and recombination of H· atoms initially trapped between the γ-AlOOH planes followed by recombination at edge and surface sites. H2 production upon thermal-annealing-irradiated material shows no dependence on incident electron flux, suggesting the precursor species (H·) trapped within the bulk are long-lived.

Oxygen as an Electron Scavenger: Its Role in Electron-Induced Activation of Coadsorbed Methane Embedded in Amorphous Solid Water

Low-energy electrons are known to play a fundamental role in activating small molecules in interstellar chemistry. Here we illustrate the electron-induced activation of the inert molecule methane while sandwiched between two 50 monolayers thick layers of amorphous solid water (ASW) on ruthenium substrate at 25 K by employing externally supplied low-energy electrons (5 eV) under ultrahigh vacuum conditions. We demonstrate how electron transmission through ASW layers under cryogenic conditions is strongly affected in the presence of cosandwiched oxygen molecules. We conclude that the resonant nature and direct electron attachment process leads to a higher degree of conversion in the presence of embedded oxygen molecules along with methane. Cross sections ranging from 1 × 10–18 to 1 × 10–19 cm2/electrons were obtained from the post-irradiation temperature-programmed desorption spectra.

Photocatalytic chemistry of methanol on rutile TiO₂(011)-(2 × 1).

Photocatalytic chemistry of methanol on the reconstructed rutile TiO2(011)-(2 × 1) surface upon 266 nm and 400 nm light excitation has been investigated quantitatively using the post-irradiation temperature-programmed desorption (TPD) method. Photochemical products such as formaldehyde, methyl formate and water, which result from the recombination of surface bridging hydroxyls through the abstraction of lattice oxygen atoms, have been identified under both 266 nm and 400 nm light irradiation. However, ethylene is detected only under 266 nm light irradiation. Through an analogy experiment, ethylene production is attributed to the photochemistry and the following thermochemistry of formaldehyde. The absence of the ethylene signal under 400 nm light is consistent with the significantly lower conversion at this wavelength compared with 266 nm. The photocatalytic reaction rate of methanol is also wavelength dependent. Possible reasons for the photon energy dependent phenomena have been discussed. This work not only provides a detailed characterization of the photochemistry of methanol on the rutile TiO2(011)-(2 × 1) surface, but also indicates the importance of photon energy in the photochemistry on TiO2 surfaces.

Excitation Wavelength Dependence of Photocatalyzed Oxidation of Methanol on TiO2(110)

Post-irradiation temperature-programmed desorption (TPD) has been used to study the photocatalyzed oxidation of methanol on TiO2(110) surface under the irradiation of 360, 380 and 400 nm light. The photocatalytic process initiated by ultraviolet light of different wavelength are similar. Methanol has been photocatalytically converted into formaldehyde, and the released hydrogen atoms transfer to the neighboring twofold coordinated oxygen to form bridging hydroxyls. The reaction rate, however, is strongly wavelength dependent. The reaction rate under 360 nm light irradiation is 4.8 times of that in the case of 400 nm exposure, consistent with a previous femtosecond time-resolved absorption measurement on TiO2 which shows the faster charge carrier recombination in the near-band-gap than the over-band-gap excitation. So far, the underlying factors which govern the excitation wavelength dependence of photocatalytic activity of TiO2 and other photocatalysts remain unclear, and future studies are needed to address this important issue.

Dynamics of Dissociative Electron–Molecule Interactions in Condensed Methanol

We have investigated the dynamics of low-energy (1–20 eV) electron-induced reactions in condensed thin films of methanol (CH3OH) through both electron-stimulated desorption (ESD) and postirradiation temperature-programmed desorption (TPD) experiments conducted under ultrahigh vacuum conditions. Results of ESD experiments, involving a high-sensitivity time-of-flight mass spectrometer, indicate that anion (H–, CH–, CH2–, CH3–, O–, OH–, and CH3O–) desorption from the methanol thin film at incident electron energies below about 15 eV is dominated by processes initiated by the dissociation of temporary negative ions of methanol formed via electron capture, a resonant process known as dissociative electron attachment (DEA). However, postirradiation TPD investigation of radicals, especially •CH2OH and CH3O• remaining in the methanol thin film, demonstrates that electron impact excitation, not DEA, is the primary mechanism by which the radical–radical reaction products methoxymethanol (CH3OCH2OH) and ethylene glycol (HOCH2CH2OH) are formed. This apparent dichotomy between the results of ESD and postirradiation experiments is attributed to the low DEA cross section for methanol compared to that of species such as halomethanes. Our results suggest that for molecules such as methanol, low-energy electron-induced electronic excitation, rather than DEA, plays a dominant role in ionizing radiation-induced chemical synthesis in environments such as the interstellar medium.

Low-energy electron-induced chemistry of condensed methanol: implications for the interstellar synthesis of prebiotic molecules.

In the interstellar medium, UV photolysis of condensed methanol (CH3OH), contained in ice mantles surrounding dust grains, is thought to be the mechanism that drives the formation of "complex" molecules, such as methyl formate (HCOOCH3), dimethyl ether (CH3OCH3), acetic acid (CH3COOH), and glycolaldehyde (HOCH2CHO). The source of this reaction-initiating UV light is assumed to be local because externally sourced UV radiation cannot penetrate the ice-containing dark, dense molecular clouds. Specifically, exceedingly penetrative high-energy cosmic rays generate secondary electrons within the clouds through molecular ionizations. Hydrogen molecules, present within these dense molecular clouds, are excited in collisions with these secondary electrons. It is the UV light, emitted by these electronically excited hydrogen molecules, that is generally thought to photoprocess interstellar icy grain mantles to generate "complex" molecules. In addition to producing UV light, the large numbers of low-energy (< 20 eV) secondary electrons, produced by cosmic rays, can also directly initiate radiolysis reactions in the condensed phase. The goal of our studies is to understand the low-energy, electron-induced processes that occur when high-energy cosmic rays interact with interstellar ices, in which methanol, a precursor of several prebiotic species, is the most abundant organic species. Using post-irradiation temperature-programmed desorption, we have investigated the radiolysis initiated by low-energy (7 eV and 20 eV) electrons in condensed methanol at - 85 K under ultrahigh vacuum (5 x 10(-10) Torr) conditions. We have identified eleven electron-induced methanol radiolysis products, which include many that have been previously identified as being formed by methanol UV photolysis in the interstellar medium. These experimental results suggest that low-energy, electron-induced condensed phase reactions may contribute to the interstellar synthesis of "complex" molecules previously thought to form exclusively via UV photons.

Photochemistry of methyl bromide on the α-Cr 2O 3(0001) surface

The photochemical properties of the Cr-terminated α-Cr 2O 3(0001) surface were explored using methyl bromide (CH 3Br) as a probe molecule. CH 3Br adsorbed and desorbed molecularly from the Cr-terminated α-Cr 2O 3(0001) surface without detectable thermal decomposition. Temperature programmed desorption (TPD) revealed a CH 3Br desorption state at 240 K for coverages up to 0.5 ML, followed by more weakly bound molecules desorbing at 175 K for coverages up to 1 ML. Multilayer exposures led to desorption at ~ 130 K. The CH 3Br sticking coefficient was unity at 105 K for coverages up to monolayer saturation, but decreased as the multilayer formed. In contrast, pre-oxidation of the surface (using an oxygen plasma source) led to capping of surface Cr 3+ sites and near complete removal of CH 3Br TPD states above 150 K. The photochemistry of chemisorbed CH 3Br was explored on the Cr-terminated surface using post-irradiation TPD and photon stimulated desorption (PSD). Irradiation of adsorbed CH 3Br with broad band light from a Hg arc lamp resulted in both photodesorption and photodecomposition of the parent molecule at a combined cross section of ~ 10 − 22 cm 2. Photodissociation of the CH 3–Br bond was evidenced by both CH 3 detected in PSD and Br atoms left on the surface. Use of a 385 nm cut-off filter effectively shut down the photodissociation pathway but not the parent molecule photodesorption process. From these observations it is inferred that d-to-d transitions in α-Cr 2O 3, occurring at photon energies < 3 eV, do not significantly promote photodecomposition of adsorbed CH 3Br. It is unclear to what extent band-to-band versus direct CH 3Br photolysis play in CH 3–Br bond dissociation initiated by more energetic photons.

Photochemistry of 1,1,1-Trifluoroacetone on Rutile TiO2(110)

The ultraviolet (UV) photon-induced photodecomposition of 1,1,1-trifluoroacetone (TFA) adsorbed on the rutile TiO2(110) surface has been investigated with photon stimulated desorption (PSD), temperature programmed desorption (TPD), and density functional theory (DFT). TFA adsorbed molecularly on the reduced surface (8% oxygen vacancies) in states desorbing below 300 K with trace thermal decomposition observed in TPD. Adsorption of TFA on a preoxidized TiO2(110) surface (accomplished by pre-exposure with 20 L O2) led to formation of a new TFA desorption state at 350 K, assigned to decomposition of a TFA-diolate species ((CF3)(CH3)COO). No TFA photochemistry was detected on the reduced surface. UV irradiation of TFA on the oxidized surface depleted TFA in the 350 K state with TFA molecules in other TPD states unaffected. PSD measurements revealed that both carbonyl substituents (CH3 and CF3), as well as CO, were liberated during UV exposure at 95 K. Postirradiation TPD showed evidence for both acetate (evolving as ketene at 650 K) and trifluoroacetate (evolving as CO2 at 600 K) as surface-bound photodecomposition products. The CO PSD product was not due to adsorbed CO, to mass spectrometer cracking of a CO-containing PSD product, or from background effects, but originated from complete fragmentation of an unidentified adsorbed TFA species. Thermodynamic analysis using DFT indicated that the photodecomposition of the TFA-diolate was likely not driven by thermodynamics alone as both pathways (CH3 + trifluoroacetate and CF3 + acetate) were detected when thermodynamics shows a clear preference for only one (CF3 + acetate). These observations are in contrast to the photochemical behavior of acetone, butanone, and acetaldehyde on TiO2(110), where only one of the two carbonyl substituent groups was observed, with a stoichiometric amount of carboxylate containing the other substituent left on the surface. We conclude that fluorination significantly alters the electronic structure of adsorbed carbonyls on TiO2(110) in such a way as to promote multiple channels of photofragmentation. Factors that dictate the partitioning between the three TFA channels are not related to photon energy (above that of the TiO2 band gap) but likely to the electronic structure of the charge transfer excited state.

Chemical Synthesis Induced by Dissociative Electron Attachment

We have investigated reactions in condensed CF2Cl2 induced by electrons of subexcitation energies under ultrahigh vacuum conditions. The yields of the CF2Cl2 radiolysis products (C2F4Cl2, C2F3Cl3, and C2F2Cl4) were determined as functions of electron energy (Ei) (∼1 to ∼4.5 eV) and electron dose (fluence) (1.5 × 1016 e/cm2 to 2.2 × 1016 e/cm2) by postirradiation temperature-programmed desorption. In general, we ascribe the formation of these radiolysis products to reactions of •CFCl2 and •CF2Cl radicals, which are generated by dissociative electron attachment (DEA) to CF2Cl2. Consistent with condensed-phase experiments, which report the electron stimulated desorption of F− ions via transient negative ion formation at incident electron energies near 4 eV, the yield of products C2F2Cl4 and C2F3Cl3 derived from reactions of •CFCl2 show maxima near ∼3 eV. The production of C2F3Cl3 and C2F4Cl2 at electron energies as low as 2 eV indicates that •CF2Cl is generated; however, the absence of a clear resonance maximum in the C2F4Cl2 yield function indicates that the production of •CF2Cl radicals via DEA is not the sole or dominant pathway for the formation of C2F4Cl2. Indeed, the variation of radiolysis product yield with electron dose suggests that the C2F4Cl2 signal may additionally be generated by reactions of CF2Cl2 with the difluorocarbene radical (:CF2), which we propose is also formed by DEA to CF2Cl2. Although numerous studies have revealed chemical damage induced by DEA, our results represent one of the first studies to unambiguously demonstrate (via a clear signature of resonance) chemical synthesis induced by this process.

Electron-Stimulated Oxidation of Thin Water Films Adsorbed on TiO2(110)

Electron-stimulated reactions in thin (<3 monolayer, ML) water films adsorbed on TiO2(110) are investigated. For electron fluences less than ∼1 × 1016 e-/cm2, irradiation with 100 eV electrons results in electron-stimulated desorption (ESD) of atomic hydrogen and small amounts of molecular hydrogen but no measurable O2. The ESD results in oxygen enrichment (“oxidation”) of the remaining film and oxidation of the oxygen vacancies originally present on the TiO2(110) surface. The postirradiation temperature-programmed desorption (TPD) spectra of the remaining water change in characteristic ways. The species remaining on the TiO2(110) after irradiation of adsorbed water films are similar to those produced by codosing water and O2 without irradiation. Annealing above ∼600 K reduces the oxidized surface, and water TPD spectra characteristic of a reduced (i.e., ion-sputtered and vacuum annealed) TiO2(110) surface are recovered. The rate of electron-stimulated “oxidation” of the water films is proportional to the...

Low-Energy Electron-Induced Oligomerization of Condensed Carbon Tetrachloride

The low-energy electron-induced chemistry of condensed CCl4 has been investigated with use of post-irradiation temperature-programmed desorption. These experiments were partly motivated by the growing interest in developing facile and economical methods for decomposing CCl4 and other halocarbons which through widespread use in industry have become potent environmental pollutants. The experimental procedure involves low-energy (50 eV) electron irradiation (fluence ≤2 × 1016 electrons cm-2) of nanoscale thin films (5 monolayers) of CCl4 grown at 100 K on a Mo(110) single crystal under ultrahigh vacuum (UHV) conditions. Results of post-irradiation temperature-programmed desorption experiments were used to identify C2Cl4, C2Cl6, C3Cl6, C4Cl6, and C5Clx as low-energy electron-induced reaction products of condensed CCl4. Two longer chain chlorocarbon oligomers with six or more carbons were also detected but not identified. Although low-energy electron-induced oligomerization reactions have been previously repor...

Adsorption and photochemistry of multilayer bromoform on ice

The adsorption and photochemistry of bromoform multilayers on and in amorphous solid water (ASW) are studied using reflection absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD), and time-of-flight (TOF) techniques. Regardless of the initial exposure, bromoform resides on top of the ASW layer. No migration of bromoform molecules into the ASW film is observed for adsorption on top of the water layer. UV irradiation at a wavelength of 266 nm results in significant desorption of photochemical fragments, reaction of photochemical products on the surface and light-induced molecular reorganization of the remaining CHBr 3, which is apparent from a comparison of pre- and post-irradiation TPD experiments. The ice-mediated C–C (C 2H 2Br 2) and C–O (CHBrO) photoproducts desorb from both the ASW surface and the Pt surface. The photoproduct C 2H 2Br 4 is formed exclusively from multilayers of CHBr 3 and desorbs only from the Pt surface.

Surface Photochemistry of Bromoform on Ice: Cross Section and Competing Reaction Pathways

The 266 nm photodissociation of bromoform adsorbed on an amorphous solid water (ASW) layer has been investigated for the first time under well-defined ultrahigh vacuum conditions. Time-of-flight (TOF) measurements indicate direct release of gas-phase Br, CHBr2, Br2, and CHBr species, with potential implications for stratospheric chemistry. Furthermore, new, ice-surface-mediated C-C (C2H2Br2) and C-O (CHBrO, CO) species are revealed in postirradiation temperature programmed desorption (TPD) and reflection absorption infrared (RAIR) spectra. A cross section of approximately 5 x 10(-20) cm2 is determined for bromoform photodissociation at 266 nm based on the integrated area of both the TOF spectra of Br and Br2 and the postirradiation TPD curves of CHBr3. The involvement of the free, non-hydrogen-bonded water groups at the ASW surface in the formation of the photoproducts is evident from the RAIRS results.

Low-Energy Electron-Induced Chemistry of CF2Cl2: Implications for the Ozone Hole?

We report on the first direct investigation of the low-energy electron-induced production of neutral species from the chlorofluorocarbon CF2Cl2, commonly known as Freon-12 or CFC-12. Our experiments were motivated by a newly proposed hypothesis, which suggests that low-energy electrons produced by cosmic rays, in addition to UV−vis photons from the sun, interact with chlorofluorocarbons to produce chlorine atoms that subsequently destroy ozone in the Antarctic. Our experimental procedure involves low-energy (5−100 eV) electron irradiation of nanoscale thin films (∼10 Å thickness) of CF2Cl2 grown at 100 K on a molybdenum single crystal in an ultrahigh vacuum chamber (p ∼ 1 × 10-10 Torr). Post-irradiation temperature-programmed desorption experiments were used to identify C2F4Cl2, C2F3Cl3, C2F2Cl4, C2F3Cl, C2F2Cl2, and C2F4 as electron-induced radiolysis products of CF2Cl2. In contrast to previous studies of photon-induced dissociation, our studies of electron-induced dissociation demonstrate facile C−F bond cleavage in CF2Cl2. This finding may have implications for understanding the partitioning of Cl and F among source, sink, and reservoir gases in the stratosphere.

Surface Chemistry and Radiation Chemistry of Trifluoroiodomethane (CF3I) on Mo(110)

The surface-induced and electron-induced chemistry of trifluoroiodomethane (CF3I), a potential replacement for chlorofluorocarbons (CFCs) and chlorofluorobromocarbons (halons), were investigated under ultrahigh vacuum conditions (p ∼ 1 × 10-10 Torr) on Mo(110). Results of temperature-programmed desorption (TPD) experiments indicate that dissociative adsorption of CF3I leads only to nonselective decomposition on Mo(110), in contrast to reactions of CF3I on other metal surfaces. Desorption of CF3 radicals and atomic iodine was detected mass spectrometrically during low-energy (10−100 eV) electron irradiation of four monolayer thick films of CF3I condensed at 100 K. Results of postirradiation temperature-programmed desorption experiments were used to identify CF2I2, C2F5I, C2F6, C2F4I2, and CFI3 as electron-induced reaction products of CF3I. Except for CFI3, all of these electron-induced reaction products of CF3I have been previously identified in γ-radiolysis studies, supporting our earlier claim that tempe...

Electron-induced dissociation of tert-butyl nitrite adsorbed on Ag([formula omitted

The electron-induced chemistry of tert-butyl nitrite (TBN, (CH3)3CONO), adsorbed on Ag(111), or over a CH3OH spacer layer, was studied at 90 K using three kinds of measurements––the time dependence of ejected fragments during 70 eV electron irradiation, temperature-programmed desorption (TPD) after irradiation, and X-ray photoelectron spectroscopy before and after irradiation. Only NO is detected during 70 eV electron irradiation, and the initial total cross-section for loss of TBN is quite large, 3.3×10−15 cm2. Post-irradiation TPD, after dissociating ∼90% of a saturated TBN monolayer, reveals residual TBN and a number of products, including NO, C4H8 (isobutene), CH3COCH3 (acetone), (CH3)3COH (t-butyl alcohol), CO and H2O. Interestingly, there is no evidence for H2 in TPD. Illustrating a central role for the Ag(111) substrate, electron-induced dissociation of monolayer TBN adsorbed over 10 ML of methanol was less efficient, by a factor of 4, than 1 ML TBN on clean Ag(111).

Charge transfer photodissociation of phenol on Ag(111)

The photochemistry of phenol on Ag(111) has been investigated by post-irradiation temperature programmed desorption (TPD). Ultraviolet (UV) irradiation at 355 and 266 nm was found to affect only the chemisorption layer in direct contact with the metal surface, while leaving the multilayer virtually intact. The main photoinduced reaction was found to be photodissociation of the O–H bond of phenol. Two new peaks were observed at the mass of phenol in the post-irradiation TPD spectrum at 335 K and 455 K. These peaks were assigned to the recombinative desorption of phenoxy with the hydrogen from O–H bond photodissociation and from thermal C–H bond fission, respectively. The photodissociation cross section was measured at different wavelengths and coverages. A charge transfer type photodissociation mechanism was proposed, where hot electrons generated in the substrate by UV photons attach to the affinity level of the adsorbed phenol. The transition to the transient anionic potential then leads to facile dissociation of O–H bond. The affinity level of phenol has been estimated to lie at 3.2–3.5 eV above the Fermi level for the 1 ML case.

Photochemistry of methane on Cu(111)

The photochemistry of methane physisorbed on Cu(111) at 35 K has been investigated by temperature-programmed desorption (TPD). Methane is photodissociated into hydrogen, methylene, and methyl by 6.4 eV photon irradiation. Post-irradiation TPD showed new desorption peaks of ethylene at 115 and 380 K, in addition to the 430 K peak reported before. They are attributed to molecular desorption of ethylene photochemically formed from methane at 35 K, associative thermal recombination of two methylene groups, and thermal disproportional reactions of four methyl groups, respectively. The photoreaction cross-section of methane depletion is estimated to be 2.0×10 −20 cm 2.

Electron Beam Induced Damage of NaNO3 Single Crystals: An Energy, Temperature, and Quantum State Resolved Study

Electron beam induced damage of NaNO{sub 3} single crystals is examined using laser resonance enhanced multiphoton ionization detection of the neutral desorption products, post-irradiation temperature-programmed desorption (TPD), secondary electron emission microscopy (SEEM), and Auger electron spectroscopy (AES). The damage initially involves destruction of the nitrate group and production of O ({sup 3}P{sub J}) and NO ({sup 2}II) fragments with nonthermal energy distributions. Specifically, the O ({sup 3}P{sub J}) J state distribution measured at 100 eV incident electron energy is 5:1.5:0.25 for J = 2:1:0, the NO ({sup 2}II) vibrational state distribution is 1:0.56:0.35:0.40:0.23 for {nu} = 0:1:2:3:4, and the NO ({sup 2}II{sub 1/2,3/2}) rotational distribution has a high population of the upper ({sup 2}II{sub 3/2}) spin-orbit component. Production and desorption of these nonthermal fragments are dominated by the decay of {l{underscore}brace}NO{sub 3}{sup {minus}}{r{underscore}brace}*. At higher electron fluences, thermalized NO, O{sub 2}, and NO{sub 2} are also produced and released, through the NO{sub 2} is a minor product. The authors suggest that the formation and desorption of thermalized NO and O{sub 2} both involve NO{sub 2}{sup {minus}} defect states and unimolecular dissociation of NO{sub 3}{asterisk}. This is supported by the observation that the NO and O{sub 2} yields have the samemore » temperature dependence which is well described by the sum of two Maxwell-Boltzmann type equations with activation energies of 0.16 {+-} 0.03 and 0.010 {+-} 0.004 eV. O{sub 2} gas is also released in post-irradiation thermal cycling from 110 to 440 K with peaks at {approximately}260 and {approximately}340 K. The authors associate the post-irradiation TPD of O{sub 2} with reactions involving O atoms released during thermal decomposition of {l{underscore}brace}NO{sub 2}{sup {minus}}{hor{underscore}ellipsis}O{r{underscore}brace} and ONOO{sup {minus}}. The SEEM image shows damage features, and the AES spectra indicate that the irradiated region is depleted in both nitrogen and oxygen relative to Na. The elemental composition shows Na{sub 2}O as a final product of the NaNO{sub 3} radiation decomposition. The 100 eV electron beam damage cross section is at least {approximately}10{sup {minus}16} cm{sup 2}.« less