1 60th international symposium on molecular spectroscopy, talk rg03, 23 june 2005, ohio state...
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160th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
Approved for Public Release; Distribution Unlimited. AAC/PA 05-03-05-170
Mario E. FajardoAFRL/MNME, Energetic Materials Branch, Ordnance Division,
U.S. Air Force Research Laboratory, 2306 Perimeter Road, Eglin AFB, FL 32542-5910. [email protected]
Takamasa MomoseDivision of Chemistry, Graduate School of Science, Kyoto University,
Kyoto 605-8502, Japan.
* Introduction to MIS in solid parahydrogen (pH2)
* IR absorption spectra of CO monomers in solid pH2
* Crystal Field Theory (CFT) analysis & assignments
* Summary
Crystal Field Theory Analysis of Rovibrational Spectra of CO Monomers in
Solid Parahydrogen
260th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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ortho- and para-hydrogen
I.F. Silvera, Rev. Mod. Phys. 52, 393 (1980). T. Oka, Fiz. Nizk. Temp. 22, 134 (1996).
Electrostatics:
Body fixed 00 = 0.484 ea02
oH2(J=1): = (2/5) 00
= 8.69x10-41 Cm2
40 r 4
3(r)
E
Rnn(pH2) 3.8Å
E(3.8Å) 108 V/m 1 MV/cm
360th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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Rapid vapor deposition of solid pH2
M.E. Fajardo and S. Tam, J. Chem. Phys. 108, 4237 (1998).S. Tam and M.E. Fajardo, Rev. Sci. Instrum. 70, 1926 (1999).S. Tam and M.E. Fajardo, J. Low Temp. Phys. 122, 345 (2001).
Deposition conditions: Tconv = 15 K
100 ppm oH2
Tconv = 19 K
1000 ppm oH2
npH2/t = 200 mmol/hr
x/t = 3.1 mm/hr Tsub = 2.4 K 2.9 K
TpH2 4.6 K
Result: mixed fcc/hcp microstructure in as-deposited samples;can anneal to pure hcp.
460th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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12C16O/pH2 IR absorptions
13 ppm 12C16O/pH2, d=2.9 mm,deposited in 60 min @ T=2.4K.
Assignments from CFT analysis.
", ||" polarization vs. hcp c-axis"" CO in metastable fcc sites
(c) T=2.4K, annealed.
(b) T=4.8K.
(a) T=2.4K, as deposited.
wavenumber (cm-1)
2135 2140 2145 2150
log 1
0(I
0/I)
(ab
s.)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
(c)
(b)
(a)
P(2)
P(1)
Q(1)CO-oH2
(CO)n
R(0)
R(1)
R(2)S(0)
560th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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Devonshire Crystal Field Theory
Physical assumptions:
(1) Molecular center-of-mass (C.M.) remains fixed at trapping site center.
(2) Rigid, undistorted trapping site.
Potential for diatomic rotor in Oh crystal field:
Vcry() = -K4 {P40(cos ) +
(1/168)P44(cos ) cos(4)}
A.F. Devonshire, Proc. Roy. Soc. (London) A153, 601 (1936).
4
660th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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CFT analysis of 12C16O in fcc pH2
For 12C16O in fcc pH2:
Beff(pH2) 0.79 Be(gas)
E(Eg - T2g) 0.56 Be(gas)
green: K4 +12Be, -19Be
red: K4 +1Be, -1Be
Pure CFT cannot explain both observations simultaneously!
Approach: use CFT for MJ splittings, treat Beff as an adjustable parameter.
Need alternative explanation for matrix effects on rotational constants.
K4 (Bgas)
-25 -20 -15 -10 -5 0 5 10 15 20 25
ener
gy le
vels
(B
ga
s)
-6
-4
-2
0
2
4
6
8
10Eg
T2g
T1u
A1g
K4 (Bgas)
-25 -20 -15 -10 -5 0 5 10 15 20 25
tran
sitio
n en
ergi
es (
Bg
as)
0
2
4
6
8
10
R(1)
R(1)
R(0)
R(1)
R(0)
760th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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Diatomic rotor in D3h crystal field
cryrv VHH
)1()1()1(),( 212
21 JJvJJDJJBvJvE eeeerv
)()()( CO3,3CO3,33CO0,22 CCCVcry
)(12
4)(
2
1
lmlm Y
lC
six adjustable fitting parameters:vibration: e
rotation: Be, De, e
crystal field: 2, 3
860th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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CFT analysis of 12C16O in hcp pH2
constant 12C16O values (cm-1)
0 2140.295(2)b [2143.2711]c
Be 1.577(1) [1.9313]
De 0.0271(1) [0.00000612]
e d 0.0129(6) [0.01750]
2 1.026(4)
3 2.523(7)a Values in parentheses are the standard deviation (1) of the least squares fitting for the last digit.b Values in square brackets are those in the gas phase. [J.A. Coxon and P.G. Hajigeorgiou, J. Chem. Phys. 121, 2992 (2004).]c The band origin of the gas phase is calculated by e-2exe+(13/4)eye.d The ground state rotational constant is B0=Be-(1/2)e and that in the excited state is Bv=Be-(3/2)e. e Fit limited to J=0, 1, & 2 levels.
82%
4400x!
~Be
960th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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Fitting results: 12C16O in hcp pH2
obs (cm-1) calc (cm-1) obs.-calc. assignment (J',M') (J",M") pol.
2134.551 2134.552 -0.001 P(2) hcp (1,1)(2,2)
2135.204 2135.204 0.000 P(2) hcp (1,0) (2,1)
2136.741 2136.743 -0.002 P(1) hcp (0,0) (1,0) //
2137.607 2137.606 0.001 P(1) hcp (0,0) (1,1)
2140.268 2140.266 0.002 Q(1) hcp (1,1) (1,1)
2142.953 2142.953 0.000 R(0) hcp (1,1) (0,0)
2143.818 2143.818 0.000 R(0) hcp (1,0) (0,0)
2145.282 2145.279 0.003 R(1) hcp (2,1) (1,0)
2145.931 2145.930 0.001 R(1) hcp (2,2) (1,1)
2146.14 2146.142 -0.002 R(1) hcp (2,1) (1,1)
2147.12 R(2) hcp ?
2148.615 2148.617 -0.002 S(0) hcp (2,2) (0,0)
J=3 levels not included
1060th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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Energy levels: 12C16O in hcp pH2
8.73 calc
?
1160th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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CFT for CO isotopomers in pH2
Annealed samples at T = 2.4 K.
Spectra shifted by subtracting gas-phase R(0) line.
relative wavenumber (cm-1)
-15 -10 -5 0 5
log
10(I
0/I)
(ab
s.)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
12C16O
(x2)13C18O
13C16O
(c)
(b)
(a)
12C18O
(d)
isotopomer Beff(pH2)(cm-1)
Bgas
(cm-1)
Beff/Bgas
12C16O 1.577 1.9313 0.8165
13C16O 1.538 1.8462 0.8331
12C18O 1.469 1.8391 0.7988
13C18O 1.437 1.7540 0.8193
Matrix effect on rotational constant Be
depends on CO isotopic composition!(see companion talk RG04).
1260th International Symposium on Molecular Spectroscopy, Talk RG03, 23 June 2005, Ohio State University, Columbus, OH
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Summary
* CO monomers exist as hindered rotors in solid pH2.
* Detailed spectroscopic assignments accomplished using Crystal Field Theory for diatomic in D3h field.
* Obtained excellent fits to experimental data.(six parameters vs. ten energy levels) 2, 3 ~ Be
Beff(pH2) 0.8 Be(gas)De(pH2) 4400 De(gas)
* Matrix effect on rotational constant Be depends on CO isotopomer! (subject of companion talk RG04...)