the temperature dependence of the amide i band of crystallline acetanilide

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.