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The temperature dependence of the Amide I band of crystallline acetanilide
Leonor Cruzeiro
CCMAR and FCT,
University of Algarve
The acetanilide (ACN) molecule
The ACN crystal
C J Brown and D E C Corbridge, Acta Cryst 7: 711 (1954)
The ACN crystal (cont)
One ACN plane
The Amide I band of ACN
AC Scott, E Gratton, E.Shyamsunder and G. Careri, Phys Rev B 32: 5551 (1985)
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
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
Crystal dynamics at finite temperature
nm
mnmn VE
Absorption spectrum
otherwise 0
2/for /1)(
)(),(
1
1
2
REEREE
EETEA
jj
N
njnj
N
jjj
Calculated linear absorption spectrum
Solid (T=10 K), dashed (T=80 K) and dotted (T=240 K). = 40 pN.
Calculated localization versus energy
Solid (T=10 K), dashed (T=80 K) and dotted (T=240 K)
Emission spectrum
otherwise 0
2/for /1)(
/exp)(),(
1
1
2
REEREE
TkEEETEE
jj
N
njnj
N
jBjjj
Calculated emission spectrum
Solid (T=10 K), dashed (T=80 K) and dotted (T=240 K). = 40 pN.
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.
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.
