Laboratory Experiments using Low Energy Electron Beams with some Emphasis on Water Vapor Quenching

1. Laboratory Experiments using Low Energy Electron Beams with some Emphasis on Water Vapor Quenching A. Ulrich, T. Heindl, R. Krücken, A. Morozov, *J.Wieser Technische Universität München, Physik Department E12 *Coherent GmbH Air Fluorescence Workshop L‘Aquila, Italy, Feb. 2009

2. Contents • I) Comparison of “p’ experiments” and “decay time” measurements • II) The relevance of “water quenching” • III) Results of our experiments (Eur. Phys. J. D 33, 207 (2005)) Foto: J. Wieser

3. Light Production by Particle Collisions The elementary process of light production: Collisional excitation of atoms or molecules and the subsequent emission of photons: Proj + X  Proj‘ + hν Proj‘ Electron or Ion (Proj) Photon (hν) Atom or molecule

4. The simplest case of data analysis: ? n* radiative Transition ro Collisionally induced transitions Two types of measurements which should match! Measuring p’ or r0 and all Qq

5. Method for Inducing Particle Collisions E Detection Issues: Intensity vs. pressure Pulsed excitation, time resolved measurement Global light output vs. local light output (Correction for geometry effects)

6. The p’ Method: Data always have to be extrapolated to 0 pressure! The geometry of the light emitting volume will always change! There may be a background, scattered light etc. For an example: See Thomas Heindl

7. The Decay- Time Method: The exponential decay has to be extracted from: The time structure of the excitation pulse! The background signal appearing at late times after the excitation! Slowing down times of the projectiles may have to be considered! The t – axis has to be well calibrated! In case of ”TAC” spectra: “Clean” statistics

8. Tilo Waldenmaier et al.: Astro-ph Feb 2008 A. Morozov et al.: Euro Phys. J D 46, 51 (2008)

9. Intermediate summary: • Both measuring techniques have their problems: • Decay time measurements need short excitation pulses, a good dynamic range of the data, a reliable analysis and fitting procedure • The p’ measurements have the problems of variation in the geometry of the light emitting volume with pressure • Also: The “physics” connecting the two measurements may not be as simple as assumed! • In practice this may cause a conceptual problem: Should the air shower experiments be analysed via tables of p’ values for all conditions found in the atmosphere or via calculation starting from N2 data? A combination of both techniques may be desireable but conceptually wrong.

10. A Comparison for Specific Data The most frequently studied case: N2*: C-B 0-0 transition at 337nm r0 = (2.66 ± 0.1) × 107 s-1 Q0 = (1.27 ± 0.04) × 10-11 cm3s-1 Results in a p’ of p’ = 78.9 hPa with an error on the order of 4% Comparison with the same method: Tilo Waldenmaier: p’ = 92.2 hPa Difference of 14% Comparison with recent directly measured p’ values:

11. Andreas Obermeier: Diplomarbeit page 45

12. The effect of a 80 vs 100 hPa p‘ value for pure Nitrogen:

13. Pure nitrogen self-quenching vs. quenching by oxigen (air, 21%) The strong oxigen quenching relaxes the influence of the nitrogen quenching ! May be that the oxigen quenching needs more attention! Airfly: p‘=3.796 hPa; Panchesny: Q=3 and 3.4×10-10cm3/s p‘=2.9 to 3.3hPa

14. The Issue of N2* Quenching by Water Vapor: Available data (C, v=0): AIRFLY: p’=1.28 hPa Tilo Waldenmaier: p’=1.82 hPa Q=(5.43±0.12)×10-10 cm3/s Andrei Morozov: p’=1.39 hPa Q=(7.1±0.7) ×10-10 cm3/s The difference between AIRFLY and Andrei Morozov is only about 8% The data were recorded at up to 25 hPa and 1.4 hPa, respectively !

15. About water vapor in the atmosphere Maximum amount of water: 3 to 30 g/m3 for –10 to 30 dec C

16. Result: The 0 and 4 km altitude cases of water content in air at 60% rel. humidity: From 2.2 to 22 hPa partial pressure!

17. An overview over the “budged” of quenching data: So far we have been working with quenching data – so the data are shown and compared in the “quenching world” and only for the C(v=0) level: Optical decay rate: 2.66×107 1/s N2* quenching by N2: Q=1.27×10-11 cm3/s N2* quenching by O2: Q=30×10-11 cm3/s N2* quenching by H2O: Q=71×10-11 cm3/s Two scenarios: Ground-level, 30 deg. C., 60% rel. hum., 1000 hPa total pressure  Max. Intensity effect due to water vapor: Iwet/Idry = 0.84; 16% effect 4km - level, -10 deg. C., 60% rel. hum., 600 hPa total pressure  Max. Intensity effect due to water vapor: Iwet/Idry = 0.86; 14% effect Example: I ~ 1/(1+(26N2 + 165O2 + 42H2O)/2.66)

18. Experiments using low energy electron beam excitation:

19. Aspects concerning water vapor measurements: • Nitrogen or air with a well defined water concentration is difficult to prepare • Water vapor is adsorbed or released from the walls of the target cell • Water vapor pressure is difficult to measure accurately • UV light and the beam may dissociate water molecules • Some solutions: • Gold covered walls of the target cell • Concentration measurement with a high precision capacitive manometer

20. Related time spectrum with fit

21. C (v=0) quenching data C (v=1) quenching data

22. Future experiments that could be performed: A) A p’ measurement with reduced geometry problems Ulbricht sphere p e-gun sensitive USB spectrometer target cell fiber optics Expected results: Rel. Intensities of the bands, p’ values, absolute yield values B) Measurement of the quenching constant for O2 if it seems to be necessary ? It would / will require a shorter electron beam pulse (Photocathode ?)

23. Thank you for your attention !