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The temperature dependence of the Amide I band of crystallline acetanilide
Leonor Cruzeiro
CCMAR and FCT,
University of Algarve
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The acetanilide (ACN) molecule
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The ACN crystal
C J Brown and D E C Corbridge, Acta Cryst 7: 711 (1954)
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The ACN crystal (cont)
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One ACN plane
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The Amide I band of ACN
AC Scott, E Gratton, E.Shyamsunder and G. Careri, Phys Rev B 32: 5551 (1985)
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Generalized Davydov/Scott Model
N
mnnnnmnm
nph
N
mnnmmnnmn
N
nnnqp
phqp
AAdFH
RVH
AAAAJAAH
HHHH
1,int
1,1
int
ˆˆ),(ˆ
})({
ˆˆˆˆˆˆ ˆ
ˆˆˆ
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A more realistic interaction Hamiltonian?
otherwise 0
20 and ||for cos ||
),(
ˆˆ),(ˆ
nmmaxnmmax
1,int
RRRRRR
dF
AAdFH
Nm
On
Nm
On
nmnm
N
mnnnnmnm
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Crystal dynamics at finite temperature
nm
mnmn VE
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Absorption spectrum
otherwise 0
2/for /1)(
)(),(
1
1
2
REEREE
EETEA
jj
N
njnj
N
jjj
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Calculated linear absorption spectrum
Solid (T=10 K), dashed (T=80 K) and dotted (T=240 K). = 40 pN.
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Calculated localization versus energy
Solid (T=10 K), dashed (T=80 K) and dotted (T=240 K)
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Emission spectrum
otherwise 0
2/for /1)(
/exp)(),(
1
1
2
REEREE
TkEEETEE
jj
N
njnj
N
jBjjj
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Calculated emission spectrum
Solid (T=10 K), dashed (T=80 K) and dotted (T=240 K). = 40 pN.
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Two different explanations
Previous: low energy peak comes self-trapped states, high energy peak from delocalized, free exciton states. Present: low energy peak comes from strongly bonded ACN molecules, higher energy peak comes from weakly bonded (length, orientation) ACN molecules. Both peaks come from localized states, but none is self-trapped.
Previous: provides a quantitative description of the temperature dependence of the lower energy peak, but not of the higher energy one. Present: provides a semi-quantitative description of the temperature dependence of the full linear absorption spectrum.
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Acknowledgements
Paulo Afonso Lopes, CITI, UNL.
Holly Freedman, Biophysics, CCMAR, UAlg.
Milipeia, University of Coimbra.
Partial support from the Portuguese Foundation for Science and Technology (FCT, Portugal) is acknowledged.
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