Temperature Dependence of the UV Fluorescence Yield in … · 2012. 1. 23. · Temperature...

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


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<∼


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)


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


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;


• 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).

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 = − ±


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.


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


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


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


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


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)


Pereira et al., Eur. Phys. J D 56 (2010) 325

Time spectra, 2P(0,0) [337,1 nm] in N2


(Pereira et al., 6th AFWS, L’ Aquila, Italy, Feb. 2009)


( )( )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 = ±


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

− −=



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


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


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.


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 .


• 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).

Temperature Dependence of the UV Fluorescence Yield in … · 2012. 1. 23. · Temperature...

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