Transcript Kouzov_ISMS2013

DETECTION AND INTERPRETATION OF
COLLISIONAL TRANSFER AND ROTATIONAL
ANISOTROPY FINGERPRINTS
IN RESONANT FOUR-WAVE MIXING SPECTRA
P. RADI and P. MAKSYUTENKO
Paul Scherrer Institute, CH-5232 Villigen, Switzerland
D. KOZLOV
A.M. Prokhorov General Physics Institute,Russian Academy of Sciences, Vavilov
str. 38, 119991 Moscow, Russia
A. KOUZOV
Saint-Petersburg State University, Saint-Petersburg 198504, Russia
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Acknowledgments
Swiss Federal Office of Energy
 Swiss National Science Foundation
(200020_124542/1)
 Russian Foundation for Basic Research
(## 11-02-01296 and 11-03-00448)

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Two-color resonant four-wave mixing (TC-RFWM) occurs when two pump
beams    and one probe beam  3 , all tuned to dipole-allowed
1
2
transitions, are crossed in a weakly absorbing medium. As the result, a
beam at 4  3 is generated in the direction k  k  k  k
4
1
2
3
(phase matching condition) .
Degenerate (one-color) case: 1   2  3   4
.
( 3)
I ~ I1I 2 I 3 |  res
2
|

e1 , 1

e2 ,2

k

  1  20

e3 , 3

e4 ,4
3
Advantages






Nonintrusive, sensitive,
molecule-selective tool
High spatial and spectral
resolution
Saturation control
Flexible polarization setup
Unique possibility to study
state-to-state transfer
Sensitivity to anisotropy of
angular momentum and
velocity distributions
Widely used for diagnostics
of hot gases, flames, reacting media
Limitations


Selective to dipole-allowed
transitions only
Weakly absorbing media
RFWM applications
 State-resolved rotational relaxation
rates induced by collisions in gaseous
media
 Angular momentum anisotropy
induced by optical pumping or chemical
reaction
“Polarization- and time-resolved DFWM spectroscopy of the
A 2Σ+- X 2Π(0-0) transitions of nascent OH radicals generated
by 266 nm laser photolysis of H2O2”
J. Raman Spectroscopy (2013).
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Outline of Theoretical Approach
1. Irreducible Spherical Tensors (no Cartesean
matrices)
Novel Features
2. Line-Space Formalism
{ f i }(qr )  N
rq
C
 Ji M i J f M f  f J f M f  i J i M i
MiM f
A( r ) | B ( r )
 Tr 0 ( A( r ) , B ( r ) )
3. Exact Treatment of Rotational Relaxation by

Collisions (Nonsecular Relaxation Matrices  (r ) (r=0,1,2) )
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Conventional 3-level schemes for TC-RFWM
generation
fif 'i '   ff ' ii'fifi
1
2
UP
3
4
SEP
Unfolded, or Ξ
Zare et al, J. Chem. Phys. 1994-1997
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Satellite generation by collisions (isotropic
gaseous media)
PSI, 1997
Relaxation
n1
n3
1
4
 2 3
m3
m1
Relaxation
Grating contributions
(r )
{m m}
{
( r ) -1 nn
mm
}
r  0,1,2
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Decoupling Procedures
I ~ I1I 2 I 3 |  res
( 3) 2
|
Isotropic medium:

 ( J )  0 ( J )
Zare et al, J. Chem. Phys. 1994-1997
 res
( 3)
 B1 B2 
    D
 Gr (e1 , e2 , e3 , e4 )Sr ( J i , J f , J n ) Lr (, )
D r 0,1, 2
   
Gr (e1 , e2 , e3 , e4 )  ({e1(1)  e4(1) }( r ) ,{e3(1)  e4(1) }( r ) )
Anisotropic medium
Vaccaro et al, 1997-2009
 res
( 3)
 B1 B2 
 (G
D K 0,1, 2..
(K )
, Ti
(K )
) S KD ( J i , J f , J n ) LD ( )
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Unusual features of collision-induced resonances
obtained in continuous –wave regime
•They are as sharp as the allowed UP/SEP lines
This contrasts with the diffuse collision-induced IR/Raman lines
No other spectroscopic tool can produce a direct
information on the collisional state-to-state transfer
rates
•Their intensities decrease considerably slower than the
squared state-to-state rates as predicted by the
perturbation theory
N ( r ) |  1 || N '( r )
Perturbation theory
 1 /  ( r ) ( n  n' )
 nn' /  nn  n 'n '
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Main and satellite resonances in the OH spectrum
P.P. Radi et al, Chem. Phys. Lett. 265, 271 (1997).
OH: (0-0) band of A2+-X2
N”
5
4
3
R1(3)
R1(6)
R1(7)
R1(9) R1(10+8)
R1(4)
R2(6)
R1(2)
R2(7)
R 2(8)
R1(3)
R2(4)
R2(5)
R2(3)
R1(1)
RET

2
x 50
N’
6
5
4
R1(5)
Relative intensity / arb. units
 
P1(5)
R1(5)
R1(4)
PUMP P1(5): 32235.95 cm-1
R21(5)
32450
32500
32550
32600
32650
probe frequency / cm-1
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Measured and calculated TC-RFWM peak intensities of OH
P.P. Radi and A.P. Kouzov, SPIE Proceedings 4460 144 (2002)
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Collision-induced TC-RFWM lines of NH radical in
ammonia-air flame demonstrating collisional spin-flip
transfer
0
Fixed probe:
Qn(4), n=1,2,3
3П
0
Q1(K)(1-0)10
9
8
7
6
5
Fixed probe
transition
(0-0) band
(initial state)
4 3
1 2
Q1(4)
3Σ-
3П
2
10
9
Q3(K)(1-0)
8
7
6
5
4
3
Q3(4)
3П
1
10
Q2(K)(1-0)
9
8
7
6
5
4
3
2
Q2(4)
32700
32720
32740 32760 32780 32800
Wavenumbers /cm-1
Pump Laser Scan (1-0)
32820
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TC-RFWM as a tool to study anisotropy of
angular momentum orientation

Anisotropic states i (J )
i 
 (T
(K )
(i ), { i  i }( K ) )
K  0 ,1, 2...
State multipoles:
K=0 scalar term; K=1 –orientational term; K=2 alignment, etc.
Anisotropy considerably changes the polarization dependence and can
induce signals at the “forbidden” (e1e2e3e4)=(YYYX) polarization geometry
Laser-induced anisotropy: direct pumping of the i-state; photolysis
Laser polarization orientation
T (K ) 
Molecular velocity orientation
K
()
( )
(K )

(
i
){
C
(

)

C
(

)}
 
D
V
  0 , 2;  0 ,1,...
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Anisotropy produced by a chemical
reaction
is a more challenging problem since the anisotropy of the states of
products is featured both in the angular momentum and velocity
distributions. The latter manifests in the Doppler-splitted shapes.
Laser photolysis
at 266nm
H 2O2   L  OH  OH
(K ) 
T (v )  T ( K ) (| v |)
Correlations  K between photofragment characteristics
Dixon, J. Chem. Phys. 85, 1866 (1986)
 ,
0
02
0
22
(v-MFI(ED))
 202 (j-ED )
recoil velocity
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 01
, 111 ,  222 (j-ED-v)
angular momentum
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TC-RFWM Doppler shapes
L( ) |
2
A
P
(


/
kv
)
|
 nn
0
n  0 ,1, 2...
v0  2(L  ED ) / m
Because of a more sophisticated polarization setup, TC-RFWM
opens up wider opportunities to study photolysis-induced anisotropy
than LIF does. Particularly, RFWM gives direct information on the
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helicity coefficients  01
, 111 inaccessible by plane-polarized LIF.
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XXXY
XYXY
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Experimental evidence of the OH helicity at
H2O2 photolysis
 
j v

j
266 nm
OH
OH
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Conclusions
1. Satellite RFWM resonances are induced by the rotational state-to-state
transfer affected by the phase-sensitive (orientation and alignment)
effects. Their study give a unique opportunity to direct spectroscopic
measurements of the collisional inelastic processes.
2. RFWM spectroscopy is a promising tool to study molecules and radicals
with rotational and translational anisotropy induced by optical pumping or
by photolysis
Problems yet unsolved
Isotropic gases
1.
2.
1.
2.
Optimization of the polarization setup to extract the cross correlation
times N | ( r )1 | N ' (r  0,1,2)
More sophisticated models of the rotational relaxation matrices are
needed
Anisotropic media
k 2
Normalization procedure to obtain absolute values of |  lm |
Elaboration of experimental RFWM approaches which give the signs of
correlation coefficients
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Thanks for your attention!
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OH level
structure
Attal-Tretout et al. Mol. Phys. 73, 1257 (1991)
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