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A COPY OF CREATIVE RESEARCH ENTERPRISES’ PRESENTATTION by Sheo S. Prasad

A COPY OF CREATIVE RESEARCH ENTERPRISES’ PRESENTATTION by Sheo S. Prasad. At the FALL 2001 AGU MEETING. TABLE OF CONTENTS. ABSTRACT BACKGROUND RECENT DEVELOPMENTS EVEN MORE RECENT DEVELOPMENTS ( since the abstract was submitted) SUMMARY & CONCLUSIONS URGENT TASKS AHED. ABSTRACT.

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A COPY OF CREATIVE RESEARCH ENTERPRISES’ PRESENTATTION by Sheo S. Prasad

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  1. A COPY OF CREATIVE RESEARCH ENTERPRISES’ PRESENTATTIONbySheo S. Prasad At the FALL 2001 AGU MEETING Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  2. TABLE OF CONTENTS • ABSTRACT • BACKGROUND • RECENT DEVELOPMENTS • EVEN MORE RECENT DEVELOPMENTS (since the abstract was submitted) • SUMMARY & CONCLUSIONS • URGENT TASKS AHED Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  3. ABSTRACT • O3(X1A1) with v high enough to produce N2O is not generated in O(3P), O2 recombination • The possibility that some form of excited O3, resulting either directly or indirectly from O(1D), O2 recombination, produced N2O in Zipf-Prasad experiment cannot be ruled out at least for now. More experiments are needed. • Pending those experiments, from an analysis of four experiments it is concluded that N2O is a product in the reactions of electronically excited O3(1B2) and O3(2 1A1) with N2 and in the photolysis of O3N2 dimer Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  4. IMPORTANCE OF N2O - O3 CONNECTION • O3 & N2O are two very important constituents of the atmosphere. Both are greenhouse gases and O3 shields the biosphere from harmful UV-A and UV-B. There is also a destructive relationship between the two since N2O is the dominant in situ stratospheric source of NO. • While the sources of the two gases are currently thought to be quite different, analyses of several experiments have suggested that some types of excited O3 might form N2O. • An O3-N2O connection can be potentially important due to the stated destructive relationship. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  5. EVOLUTION OF N2O-O3 CONNECTIONHas twists & turns very familiar in path to progress! • Prasad,1981; Electronically excited metastable triplet O3 was thought to be a possible source of N2O based on experiments that appeared to support formation of triplet O3 in O, O2 recombination • Prasad,1994; 10 experiments further support N2O formation via some type of excited O3. But, by this time the prospect of metastable excited triplet was lost. So, excited O3(X1A1, very high v) from O, O2 recombination was proposed as N2O source • Zipf & Prasad, 1998; O3(X1A1, very high v) appeared to explain the high yield of N2O in Zipf-Prasad experiment • 2001; Role of O3(X1A1) eliminated (Estupinan). But, electronically excited O3 may be forming N2O after all ! (Prasad) Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  6. THE RECENT DEVELOPMENT:ESTUPINAN’S NON-DETECTION OF N2O IN N2/O2/O3 PHOTOLYSIS AT 532 NM • Estupinan’s non-detection in this experiment does not mean that N2O is not produced by O3(X1A1, sufficiently high v). Instead, it means that the high vibration needed to produce N2O is not generated when O3(X) from O(3P) , O2 recombination. • Thus, the origin and identity of the species that produced N2O in Zipf-Prasad experiment remains an important chemical physics and atmospheric chemistry problem to be solved by more experiments. At least for now, that species may still be some form of excited O3 resulting either directly or indirectly from O(1D), O2 recombination. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  7. MORE RECENT DEVELOPMENT:AN ANALYSIS OF THE SECOND SET OF ESTUPINAN’S EXPERIMENT AND THREE OTHER PREVIOUS EXPERIMENTS Pending experiments needed to better understand Zipf-Prasad’s, the rest of the presentation will dwell on an analysis of experiments by • Estupinan on N2/O2/O3 photolysis at 266 nm • Gaedtke et al on on N2/O2/O3 photolysis at 254 nm • Kajimoto & Cvetanovic on N2/O2/O3 photolysis at 254 nm and at N2 pressures from 27 to 113 atmospheres • DeMore & Raper in liquid phase and 200 to 350 nm using a model of N2O quantum yield that explains the yield observed in all these experiments encompassing a very wide range of pressures and radiation wavelength and relative N2, O2 & O3 amount Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  8. GAEDTKE ET AL EXPERIMENT SUGGEST N2O FORMATION FROM PROCESS OTHER THAN O(1D), N2 ASSOCIATION • Gaedtke et al (1973) found N2O formation in photolysis of N2/O2/O3 mixture at 254 nm and 1 atm pressure and determined 2.7x10-36 as the the rate coefficient for the O(1D) + N2 + M -> N2O + M, if the observed N2O is attributed to that reaction. • Later work by Kajimoto & Cvetanovic (1975) suggested a much smaller (by factor of 7.7) rate coefficient (or, 3.5x10-37) and this smaller coefficient is currently recommended by NASA Panel. • In retrospect, Gaedtke et al experiment imply that at lower pressures N2O may form more efficiently by process (es) other than O(1D)+N2 Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  9. EFFICIENT FORMATION OF N2O BY PROCESSES OTHER THAN O(1D), N2 ASSOCIATION IS CONFIRMED BY ESTUPINAN EXPERIMENT • 28 year later, Estupinan et al found a linear variation of the quantum yield N2O in 100 to 1000 torr pressure range, N2O/PN2 = 2.1x10-6 when PN2 is in atm • If the observed N2O is attributed to O(1D), N2 association (as Estu-pinan et al did), the rate coefficient for the association reaction at 1 atm again turns out to be too large by a factor of almost 8 compared to current NASA Panel recommendation based on Kajimoto & Cvetanovic experiment. • Thus, it is urgent to search for the process(es) that could produce N2O more efficiently than the O(1D), N2 association at 1 atm. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  10. PRODUCTION FROM ELECTRONICALLY EXCITED O3 IS A LOGICAL CHOICE • None of the other species expected in N2/O2/O3 photolysis (like O2(1g) , O2(b 1)) has enough energy to produce N2O • In principle photolysis of O3 with Hartley band photons can produce vibrationally excited O2 with vibrational energy needed to possibly generate N2O. However, at 266 nm this too is not possible. • O3(X,1B1) with high v attainable in O, O2 recombination has already been eliminated • Thus, O3(1B2) + N2 -> N2O# + O2*# (where superscripts * and # represent, respectively, electronic and combined vibrational and translational excitations) may be the logical process. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  11. THE FACT THAT ELECTRONICALLY EXCITED O3 HAS LIFETIME OF MOSTLY FEMTOSECONDS SHOULD NOT CAUSE MUCH CONCERN • Possibly, when a N2 comes so close to a O3(1B2) that it might react then the close proximity perturbs the dissociation dynamics to an extent that there is time to form the transition state. • The "net" reaction may involve a hitherto unrecognized, electronically excited, O3 with shallow minimum in its potential energy surface into which a fraction of O3(1B2) may change by curve crossing • Also, after all short lived O2(B3 ) with lifetime of ps or less is known to react Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  12. RATE CONSTANT FOR O3(1B2) + N2 -> N2O# + O2*# DERIVED FROM ESTUPINAN’S N2O IS VERY REASONABLE • At any point in the irradiated region the very small but finite number density of O3(1B2) that have not as yet lost their identity is n(O3(1B2)) = J n(O3) / kdiss ; kdiss = (lifetime)-1 • The corresponding quantum yield is : (k/kdiss )n(N2) where k is the rate constant of the title reaction • With Estupinan’s N2O & lifetime = 10 fs, k = 8x10-12cm3s-1 Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  13. IF O3(1B2) FORMS N2O, THENTHE FOLLOWING SHOULD ALSO HOLD • There should be considerable N2O formation when O3 is excited to the secondary minima of the 2 1A1 or to the quasi-bound portion of the 1B2 potential energy surface thatare responsible for the Huggins bands (despite the negligible yield of O(1D) in this region). • The N2O derived in from Estupinan’s data should be consistent with that from the high pressure data of Kajimoto and Cvetanovic. From a reinterpretation of Kajimoto & Cvetanovic and DeMore & Raper experiments, using a more complete model of N2O, both constrains are found to be fulfilled (as will be now explained). Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  14. THE MODEL OF N2O USED TO REINTERPRET KAJIMOTO & CVETANOVIC AND DEMORE & RAPER DATA HAS FOLLOWING FEATURES • Quantum yield from O3(1B2) and O3(2 1A1) [Linear in pressure p] • All elements of Kajimoto & Cvetanovic’s model of N2O from O(1D), N2 association [p2 variation] • Contribution of O3N2 + hv N2O+ O2 that represents the photolysis of O3 component of the O3N2 and the O(1D), N2 association inside the dimer. [Also, p2 variation] • Details are in a preprint available for distribution to those interested. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  15. THE N2O FOR THE O3(1B2) COMPONENT FROM KAJIMOTO & CVETANOVIC AND N2O FROM ESTUPINAN DATA AGREE EXCELLENTLY Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  16. THE N2O FROM O3 EXCITED BY HUGGINS BAND AND DIMER EFFECT ARE ALSO EXPERIMENTAL REALITIES Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  17. THE ATMOSPHERIC PRODUCTION OF N2O FROM O3 EXCITED BY HUGGINS BANDS MAY BE SIGNIFICANT • Significance • Direct way of producing mass-independent heavy O-atom enrichment in N2O • Total atmospheric production (2-3)x108 N2O cm-2 s-1 is substantial A & B represent two different ways of diurnal averaging. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  18. SUMMARY & CONCLUDING REMARKS (#1) N2O is a quite possible and atmospherically significant product when O3 is excited by Huggins band (310-340 nm) photons in air (#2) Since this production may occur in the stratosphere, missing sinks of N2O are implied, if the possibility in (1) is upheld by experiments (#3) O3(X1A1) with so high v that they might produce N2O are not generated in O(3P), O2 recombination.But, this does not preclude its formation in other ways such as fluorescence from O3(1B2) (#4) The identification of the species responsible for N2O observed by Zipf-Prasad is an important chemical physics and atmospheric chemistry problem. For now at least, that species may still be some form of excited O3 resulting either directly or indirectly from O(1D), O2 recombination. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  19. EXPERIMENTAL RESEARCH TASKS THAT NEED URGENT ATTENTION • Since DeMore & Raper experiment was done in condensed phase, it is most important to study the production of N2O with high spectral resolution when gas phase mixtures of air and O3 are irradiated by Huggins band photons at various atmospherically significant temperatures and pressures, simultaneously examining the isotopic composition of the product N2O • It is also important to repeat Zipf-Prasad (ZP) and Estupinan experiments; the former with spectrally finely resolved light source spanning the range of wavelengths covered by ZP’s lamp, and the latter with O3/air ratio tending to zero. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

  20. EXPERIMENTAL RESEARCH TASKS (Cont.) • The fact that Estupinan et al experiments done with the marvels of modern laboratory techniques gave the same answer as was obtained 28 years ago with much simpler techniques available at that time shows that • the needed set of experiments can be done with relatively simple techniques available at even moderately equipped laboratories. • It is therefore hoped that this presentation will enthuse many others to experimentally check the interpretations presented here. Creative Research Enterprises’ Presentation at AGU 2001 Fall Meeting

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