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Temperature Dependence of the UV
Fluorescence Yield in Nitrogen
and in Dry Airand in Dry Air
Margarida FragaLIP-Coimbra & Departamento de Física,
Universidade de Coimbra,
Coimbra, Portugal
excv'v '' v 'v '' v 'v 'Y (P,T) A (P,T) ( TN P, )eff = τ (ph/MeV)
FluorescenceFluorescence Yield:Yield:
Two methods:Two methods:
• Time resolved measurements ' v 'v 1/ (P,T(P,T) )eff R⇒ = τ
M. Fraga, LIP-Coimbra 28thAFWS, Karlsruhe,Set-2011
• Light intensity measurements v'v v '''' 'v( ,T) YI (P,T ,) (P T) ⇒ = η λ P
excv'
v 'v ''v '
N (P,T)I
(P,T)corr
R∝
If only direct excitation is possible : v'v ''v '
1I
(P,T)corr
R∝
jj
v 'v ' XX
jv '
1(P,T) Av' eff
R k (T) f N= = +τ
∑
X j = N2, O2, H2O, Ar, CO2, …
v' v 'v '' ov'' v '
1A A= =
τ∑
Xj
N2*(C,0) products
A0v’’
N2*(C,v’>0)
N2kv’0
Xj
products
e-
Kinetic ModelKinetic Model and Decay Ratesand Decay Rates
j
v 'qX
k
j
0X
k
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 3
v'' v 'τ
N2*(B,v’’),
v’’=0,1,2,…
A0v’’
N2(X)
C0
Cv’
e-
e- 18AN7.243 10
R-3p p(hPa)
N cmT T(K)
= = ×
vv k' 'k ( pT) N (T) =
Av v
N 1
Rk '' k(
T)T) (T=
At room temperature (T0),
jj
v 'X X
v 'v ' v '
jv '(P) A k A 1
p '0
0R f pp
+
= + =
∑
j
j
X
v ',Xv ' j
1;
p ' p '
f=∑
' ' '1 N2 O2f f= +
j
jv '
v ',X v 'X
A
kp ' =
with and
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 4
When T changes and gas density is kept constant,
j jXv 'Xv v '
v '' v '
jA 1
' ()
)( )( AR T f NT
p
p Tk= + =
+
∑
2 2' ' 'air,v ' N ,v ' O ,v 'p p p
= +
00
Tp p
T=
v '8
( ) v ( ) ( )Bk Tk T < T T = > σ = σ
πµ
Temperature dependence of the quenching rate constantTemperature dependence of the quenching rate constant
Possible explanations for a negative temperature dependence of the collisional cross section (see S.
Rodrigues, 7th AFWS, Coimbra, Set. 2010) :
� The process is very exothermic
� Absence of barriers for the process
x The process is governed by very long-range attractive forces ( ) , 4nn
CV R n<∼
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 5
Dependence laws:
x The process is governed by very long-range attractive forces
? Quenching proceeds through the formation of complexes
21
ci) ( ) c exp T
T σ =
1ii) ( ) c (power law)0
T T
T
α
σ =
( ) , 4n
V R nR
<∼
Power law Power law
v ' 0.5
vv ' '( ) ( )00T
k TT
k Tα +
=
v ' v ' 0.5β = α +
v ' 0.5
v ' v 'p ' ( ) p ' ( ) 00
TT T
T
α − =
• Time resolved measurements (@ constant gas density) yield
v ' 0.5
vv ' 'k ( ) k ( )00
TT
TT
α −
=
Av v
N 1
Rk '' k(
T)T) (T=(cm3 s-1)
(hPa-1 s-1)
(hPa)
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 6
N2v ' v '
v ',( ) A
( ) )3 -1R Tk T (cm s
N
−=
• Time resolved measurements (@ constant gas density) yield
for pure N2
N2O2
v ' v ' v ',v ',
( ) A ( )( ) )N2
O2
3 -1N
N
R T k Tk T (cm s
− −= for N2/O2 mixtures
• @ constant gas density, light intensity for a given v’-v’’ band varies with T
according to (neglecting the vibrational relaxation mechanisms) :
v '
v 'v 'v ''
11
p' ( )I ( )0
corr000
p T
TTp ,T
β
∝ +
for N2/O2 (79:21)
Fraga et al., NIMA 597 (2008)
0.51
1 1
air air
0pp T Tλ λα − β
∝ + = +
for pure N2
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 7
2 2
M. Ave et al. NIM A597 (2008) 50air airv ' v 'v 'v ''
11 1
p' ( ) p ' ( )S0
0 00 0
pp T T
T TT T∝ + = +
N O2 2v ' v '
2 2air N O2 2
N O
v' v ' v 'p' p ' ( ) p ' ( )
air
00
0 0 00 0
f fp T T Tp
T T TT T
λβ β β = +
with
0.5air airλλβ = α +
Experimental results:Experimental results:
1) Light Yield measurements @ Coimbra (Fraga et al., NIMA 597 (2008)) :
• pure N2 ;
• Excitation source : α-particles from Am-241
• Wavelength: (0,0) band centered at 337 nm selected with an IF (λc =340 nm,
∆λ=10 nm);
• P = 300 – 700 hPa;
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 8
• T = -20ºC – 25º C ;
• Experimental counting rates are corrected for geometric factors, variation of
the transmission of the IF with angle of incidence and temperature, variation
of the response of the PMT with T and takes into account the spectral
distribution of light (as a function of T).
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 9
250 260 270 280 290 3000.096
0.100
0.104
0.108
0.112
0.116
0.120
Inte
nsity
(a.
u.)
336 hPa
0.060688 hPa
250 260 270 280 290 3000.028
0.030
0.032
0.034
0.036
0.038
0.040
Inte
nsity
(a.
u.)
T (K)
512 hPa
N2, 2P(0,0) band @ 337 nm
0.33 0.10β = − ± 0.43 0.16β = − ±
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 10
250 260 270 280 290 3000.048
0.052
0.056
Inte
nsity
(a.
u.)
T (K)
250 260 270 280 290 3000.80
0.85
0.90
0.95
1.00
1.05
1.10
336 hPa 512 hPa 688 hPa
No
rma
lize
d i
nte
nsi
ty
T (K)
0 0.37 0.07β = − ±
0.38 0.06β = − ±
2) Light Yield measurements - AIRFLY collaboration (M. Ave et al. NIM A597 (2008) 50,
Nozka et al., Optik 120 (2009) 619):
• Dry air @ ≈ 1000 hPa ;
• T = 240 K – 310 K @ constant gas density;
• Excitation source: 3 MeV electron VdG, DC beam, 10 μA
• Wavelengths : 284 – 429 nm using a spectrograph (ORIEL MS257) + CCD ;
M. Fraga, LIP-Coimbra 11
in A. Obermeier, 5th FW, El Escorial,
Spain, Set. 2007
in L. Nožka, 5th FW, Madrid, Set. 2007
AIRFLY chamber used in the
temperature dependence
measurements.
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 12
in M. Bohacova, 6th FW, L’Aquila, Italy,
Feb. 2009
AIRFLY results:AIRFLY results:
air
v 'v ''
v '
1( )
1p' ( )0
0
0
S p,TTp T
T TT
λα∝ +
1 f f
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 13
in M. Bohacova, 6th FW, L’Aquila, Italy, Feb. 2009
2 2' ' '
v ' N ,v ' O ,v '
1
p ( ) p ( ) p ( )0 0 0
N2 O2
air,
f f
T T T= +
( )
( )0v''
00
S p,T vs T
S p,T
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 14
in M. Bohacova, 6th FW, L’Aquila, Italy, Feb. 2009
v’ (v’,v’’) λ λ λ λ (nm) ααααλλλλ [1]
0 (0,0) 337.1 -0.35±0.01
0 (0,1) 357.7 -0.35±0.02
0 (0,2) 380.5 -0.34±0.03
0 (0,3) 405.0 -0.37±0.08
1 (1,0) 315.9 -0.19±0.03
1 (1,2) 353.7 -0.22±0.04
v’ v’’ λ λ λ λ (nm) ααααλ λ λ λ [1]
0 0 391.4 -0.79±0.03
0 1 427.8 -0.54±0.08
AIRFLY results for the measured temperature dependence parameters :
ii) For two N2+ 1N bands
[1] M. Bohacova, 6th FW, L’Aquila, Italy, Feb. 2009
i) For some N2 2P bands
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 15
1 (1,3) 375.6 -0.17±0.05
1 (1,4) 399.8 -0.20±0.08
2 (2,1) 313.6 -0.13±0.05
2 (2,3) 350.0 -0.38±0.16
2 (2,4) 371.1 -0.24±0.13
2 (2,5) 394.3 -0.20±0.14
3) Time resolved measurements @ TUM (Pereira et al., Eur. Phys. J D 56 (2010) 325)
• Excitation source: 10 keV electron-beam from an e-gun
• P = 50 hPa – 500 hPa
• T = 300 K to 210 K @ constant gas density;
• Pure N2: (0,0), (0,1), (1,0) and (1,3) bands @ 337.1, 357.7, 315.9 and 375.5 nm
respectively , selected by a monochromator + PMT;
• Mixtures O2/N2 : (0,0) band @ 337.1 nm
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 16
Emission bands of the N2 2P system at 400 hPa
(298 K). The wavelength resolution is 1 nm.
(Pereira et al., 6th AFWS, L’ Aquila, Italy, Feb.
2009)
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 17
Pereira et al., Eur. Phys. J D 56 (2010) 325
Time spectra, 2P(0,0) [337,1 nm] in N2
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 18
(Pereira et al., 6th AFWS, L’ Aquila, Italy, Feb. 2009)
Pereira et al., Eur. Phys. J D 56 (2010) 325
( )( )1
01
00
11 3 1
11 3 1
34.5 ns
35.0 ns
(298 ) 1.24 0.04 10 cm s
(298 ) 2.60 0.08 10 cm s
0k
K
Kk
− −
− −
τ =
τ =
= ± ×
= ± ×
N2v ' v '
v ',( ) A
( ) )3 -1R Tk T (cm s
N
−=
Temperature dependence of the quenching rate constants of NTemperature dependence of the quenching rate constants of N22 ((C,vC,v’=0) and (’=0) and (C,vC,v’=1) states ’=1) states
by Nby N22(X) molecules:(X) molecules:
0 0.33 0.04β = − ±
( ) ( ) 11 3 1C 1.2 0.2 10 cm s0k 298K − −= = ± ×
1 0.14 0.08β = ±
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 19
LY0 0.37 0.07β = − ±
( ) ( ) 11 3 1C 2.67 0.14 10 cm s1k 298K − −= = ± ×
( )( )
11
1
3 1
11 3 1
(298 ) 1.24 0.04 10 cm s
(298 ) 2.60 0.08 10 cm s
0k
k
K
K
− −
− −
= ± ×
= ± ×
From Rv’ vs p, @ 298 K:
From intensity measurements:
k0 increases by (13±3)% from 300 to 210 K,
k1 decreases by (5±3)% from 300 to 210 K
(Pereira et al., Eur. Phys. J D 56 (2010) 325)
Temperature dependence of the quenching rate constant of N2 (C,v’=0) state by O2:
0 0.08 0.05β = ±
N2O2
v ' v ' v ',v ',
( ) A ( )( ) )N2
O2
3 -1N
N
R T k Tk T (cm s
− −=
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 20
Pereira et al., Eur. Phys. J D 56 (2010) 325
k0,O2 decreases by (3±2)% from 300 to 210 K
( ) ( ) 11 3 1C 29.5 3.0 10 cm s20,Ok 298K − −= = ± ×
( )20,Ok 298K =
From R0,O2 vs pO2 , @ 298 K:
Comparison of Light Yield results and Time Resolved measurements Comparison of Light Yield results and Time Resolved measurements –– pure Npure N22
220 240 260 280 300
0.80
0.85
0.90
0.95
1.00
1.05
220 240 260 280 300
(b)
Nor
mal
ized
inte
nsity
336 hPa
(a)
Temperature, K
512 hPa
Temperature, K1.05
2P(0,0) band
λ = 337.1 nm
M. Fraga, LIP-Coimbra
8thAFWS, Karlsruhe,Set-2011
21
Temperature, K
220 240 260 280 300
0.80
0.85
0.90
0.95
1.00(c)
688 hPa
Nor
mal
ized
inte
nsity
Temperature, K
0
0
up0
0
( ) if 0(
C)
AI T
A k T N∝ =
+
dir up000 0
0
1I (T) C C (T)
R (T) ∝ +
-> green lines
10
1 1
0 0
( )1 0.59
( )( )
( )
k T N
A k T NI T
A k T N
++∝
+ -> red lines
1 10 1( ) ( ) ( )qk T k T k T= +
0.8
0.9
1.0
1.1
1.2
rate
co
nst
an
t (a
.u.)
k1
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 22
0.6
0.7
0.8
200 220 240 260 280 300
rate
co
nst
an
t (a
.u.)
T(K)
kq1
k10
1 10 1( ) ( ) ( )qk T k T k T= +
Comparison of Light Yield results from AIRFLY and Time Resolved Measurements Comparison of Light Yield results from AIRFLY and Time Resolved Measurements –– dry air:dry air:
2P(0,0) band, λ = 337.1 nm
A0
A0
i) If VR is neglected (C0up = 0)
-> green lines
ii) If vibrational relaxation is taken into account (red
lines) ,
101
1
( )1
( )( ) ;
k T NE
R TI T
+∝ with
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 23
1
0
( )( ) ;
( )
R TI T
R T∝
11
0
0.59dir
dir
CE
C= =
N2 O2, ,( ) A ( ) ( )1 1 N2 1 O21 N NR T +k T +k T=
N2 O2, ,( ) A ( ) ( )0 0 N2 0 O20 N NR T +k T +k T=
with
Monte Carlo simulation gives, , just as in pure N2.
Pereira et al., Eur. Phys. J D 56 (2010) 325
k1,N2 and k1,O2 show a weak T dependence ⇒ R1(T) ∼ constant
ConclusionsConclusions
• Quenching cross sections are temperature dependent;
• N2 C3Πu state:
• the lowest vibracional state, v’=0, is the one that exhibits the strongest T dependence,
both for the quenching by N2 and O2 molecules;
• Temperature dependence of the quenching constant rates of vibrational states v’=1 and
v’=2 (or of the intensities of the bands originating at v’=1 and v’=2) is weak and very
similar;
• Quenching of N2+ (B,v’=0) state in pure nitrogen (αλ=-0.82, according to Belikov et al., J. Chem.
Phys. 102 (1995) 2792) and in dry air exhibits a strong dependence on T .
M. Fraga, LIP-Coimbra 8thAFWS, Karlsruhe,Set-2011 24
• Good agreement between the temperature dependence of the UV band intensities obtained by
different techniques in different Labs.
Aspects that need further clarification:
• the different T dependences of (C, v’=0 ) and (C, v’=1,2) states
Still missing:
• The effect of humidity on the temperature dependence of air fluorescence band intensities;
• A theoretical explanation for the observed negative temperature dependence of the
quenching cross section (calculations are in progress).