Laboratory Experiments for Studying the Emission of

Nitrogen and Air

Andreas Ulrich, Andrei MorozovTechnische Universität München

Fakultät für Physik E12

4th Air Fluorescence WorkshopMay 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 N2 emission bands (experiments in Chicago and Garching)

V) Improvements

Vacuum Gas

Membrane

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 SiNx

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

Al, "Lenard"2650 nm

SiNx

300 nm

Ti, 1.1 mg/cm2

2439 nm

Tra

nsm

. (%

)

E (keV)

Experimental setup

Motivation for using low energy electrons for N2 emission studies:

High fluorescence yield at low energy

Copied from DPG-presentation 2006: Andreas Obermeier

Steel tube

Glowing gas

Silicon wafer with entrance

foil Z

Y

X

Ne, 250 hPa Ne, 500 hPa Ne, 1000 hPa

0 2 4 6 8 10 12 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Distance, mm Distance, mm Distance, mm

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

Rprod.

τ0 τc

QpRT

pVknk

ratesQuenching

p

pI

Qp

Definition

QpI

pEfI

Qp

R

RRR

Rf

ratioBranching

exc

rad

collcollrad

rad

:

'1

1

1'

:

1

1

)(

11

1

1

1

:

0

0

0

The two approaches:

0 50 100 150 200 250

1

10

100

1E3

Inte

nsity

, co

unts

Time, ns

0 10 20 30 40 500,00

0,01

0,02

0,03

0,04

0 10 20 30 40 500,00

0,01

0,02

0,03

0,04

337 nm (0 0)

Rat

e, n

s-1

N2 pressure, hPa

R = a + b×P

a = (227.8 ± 6.6) ×10-4 ns

-1

b = (43.6 ± 2.5) ×10-5 ns-1 hPa-1

R = a + b×P

a = (236.1 ± 6.7) ×10-4 ns

-1

b = (41.9 ± 2.5) ×10-5 ns-1 hPa-1

357 nm (0 1)

Rat

e, n

s-1

N2 pressure, hPa

time spectra pressure dependence

the connection

Nagano et al. astro-ph/0303193 v3 26 Aug. 2003

qkp

0

' 1

Example:

N2 2P-Band, v=0 and v=1, 337 and 316nm

τ0 = 41.7ns (for both v)

kq = 1.2×10-11 cm3/s and

kq = 2.5×10-11 cm3/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‘ = 151.7 hPa and

p‘ = 88.3 hPa, respectively (10% error)

Nagano et al. astro-ph/0303193 v3 26 Aug. 2003

?

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 N2

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 79.36 to 91.95 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.)

10

111

1

1000

'1

1

1

1

1

:mod

EFE

p

pI

pQpQ

pQF

EFEpQ

I

elExtended

d

v=0

n=1

τ0 Q1p τ1 Q1dp

Q1p

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:D2 Lamp

280 300 320 340 360 380 400 420 4400.0

0.2

0.4

0.6

0.8

1.0

1.2

S

ensi

tivity

(re

l. un

its)

(nm)

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)

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 N2 emission bands:

Comparison of Chicago and Garching data with literature values

Relative intensities of N2 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 D2 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