Laboratory Experiments for Studying the Emission of Nitrogen and Air Andreas Ulrich, Andrei Morozov Technische Universität München Fakultät für Physik E12 4th Air Fluorescence Workshop May 17-20, 2006, Prague - Pruhonice

I)Excitation of dense gases with low energy electron beams II)Shape of the excited volume III)Correlation of quenching rate constants k and p‘ values IV)Intensity ratios of N 2 emission bands (experiments in Chicago and Garching) V)Improvements

I) Excitation of dense gases with low energy electron beams Typical parameters: Electron energy:15 keV Beam current:10 μA average Pulses:5 ns minimum Gas pressure:0.1 – 2 bar Membrane:300 nm SiN x

Experimental setup

Motivation for using low energy electrons for N 2 emission studies: High fluorescence yield at low energy Copied from DPG-presentation 2006: Andreas Obermeier

II) Shape of the excited volume The shape can be modelled using the program: „casino“ ( P. Drouin, A. R. Couture, R. Gauvin, P. Hovington, P. Horny, H. Demers, Univ. de Sherbrooke, Quebec, Canada (2002) ) This will be important for absolute emission measurements using low energy electron beams!

III) Correlation of quenching rate constants k and p‘ values R prod. τ0τ0 τcτc

The two approaches: time spectrapressure dependence the connection Nagano et al. astro-ph/ v3 26 Aug. 2003

Example: N 2 2P-Band, v=0 and v=1, 337 and 316nm τ 0 = 41.7ns (for both v) k q = 1.2× cm 3 /s and k q = 2.5× cm 3 /s, respectively Results in p‘ = 74.6 hPa and p‘ = 35.8 hPa, respectively (10% error) Morozov et al. Eur. Phys. J. D 33, 207 (2005) In contrast to: p‘ = hPa and p‘ = 88.3 hPa, respectively (10% error) Nagano et al. astro-ph/ v3 26 Aug ?

Potential reasons for the discrepancy: Systematic errors ? Collisional mixing of the vibrational levels ? See: J. M. Calo and R. C. Axtmann, J. Chem. Phys. 54, 1332 (1971) C, v=0, 1 B, v=0, 1, etc. Non radiative quenching Collisional quenching of v – levels by N 2 Radiative transition A model worked out by Andrei Morozov showed an increase of the p‘ value for the 337nm (v‘=0 to v=0) transition from to hPa using the data given in the publication by Calo and Axtmann. (I(p) modelled with and without coll. quenching of v levels and then fit using the regular formular.)

v=0 n=1 τ 0 Q 1 p τ 1 Q 1d p Q1pQ1p

First test of the influence of vibrational relaxation via collisions: Classical model, new model with vibrational relaxation, data from new model fit with classical model

Intensity ratios of nitrogen emission bands Spectral response of McPherson 218. Preliminary measurements: Black: W Strip-lamp Blue: W Strip- lamp + UG11 Red: D 2 Lamp

Spectral response of the „Rome“ spectrometer Measured with a calib. halogen and a Hg pen-ray lamp, respectively

Spectrum of air recorded using electron beam excitation, McPherson model 218 VUV monochromator and photon counting:

Comparison of spectra of laboratory air excited by 10 keV photons (photoelectrons) and 10 keV electrons (APS Chicago and e - beam Graching)

Detail:

Comparison of the weakest and strongest lines analysed (Garching data):

Relative intensities of N 2 emission bands: Comparison of Chicago and Garching data with literature values

Relative intensities of N 2 emission bands: Comparison of Chicago and Garching data with literature values Log – scale:

Analysis of the same Garching- data, two persons independently

Improvements: We have bought a 100 W calibrated halogen lamp (LOT / Heraeus) We will borrow a new calibrated D 2 from GSI-Darmstadt (Plasma physics group) Measurements of the absolute photon flux will be performed Pressure dependences should be measured for the ~10 keV electrons Acknowledgement ! Many thanks to Paolo Privitera, Hans Klages and all their coworkers for inviting me to participate in the Chicago experiment and KfA-Karlsruhe for paying for the trip. Thanks to Reiner Krücken and MLL for supporting my trip to this conference. I want to thank Jochen Wieser (TuiLaser/Coherent) for his help with the experiments and the apparatus, in particular the very stable power supply. Thank you for your attention