GAS PHASE RAMAN SPECTRUM OF TCNQ AND PRESSURE DEPENDENCE OF THE MODES IN CRYSTALS OF TNCQ°

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GAS PHASE RAMAN SPECTRUM OF TCNQ AND PRESSURE DEPENDENCE OF THE MODES IN

CRYSTALS OF TNCQ°

C. Carlone, N. Hota, H. Stolz, M. Elbert, H. Kuzmany, H. Hochheimer

To cite this version:

C. Carlone, N. Hota, H. Stolz, M. Elbert, H. Kuzmany, et al.. GAS PHASE RAMAN SPECTRUM OF

TCNQ AND PRESSURE DEPENDENCE OF THE MODES IN CRYSTALS OF TNCQ°. Journal

de Physique Colloques, 1981, 42 (C6), pp.C6-323-C6-325. �10.1051/jphyscol:1981694�. �jpa-00221631�

JOURNAL DE PHYSIQUE

CoZZoque C6, supplgment au n o 12, Tome 42, decembre 1981 page c6-323

GAS PHASE RAMAN SPECTRUM OF TCNQ AND PRESSURE DEPENDENCE OF THE MODES IN CRYSTALS OF TNCQ'

C. Carlone , N.K. ~ o t a * , H . J . ~ t o l z * * , M. ~ l b e r t * * * , H. ~ u z m a n y ~ * and H.D. Hochheimer*"

Ddpmtement de Physique, UniversitQ de Sherbrooke, Sherbrooke, Que'bec, Canada, J I K 2RI.

*Ddpartement de chimie, CoZZBge militaire royaZ, St-Jean, &&bee, Canada.

**Max-PZanck-Institut fiir Festkorperforschung, 7000 Stuttgart 80 , ^{F.R. G.}

***Ludwig Boltzmann Institut f i i ~ festkorperforsehung, and Institut fiir festkorper- physik der Universitiit Wien, Wien, Austria.

A b s t r a c t . - The Raman spectrum of gaseous TCNQ was o b t a i n e d . V i b r a t i o n s were d e t e c t e d a t 40, 76, 145, 340, 1225, 1454, 1606 and 2230

2) em-'. The pres- s u r e dependence of t h e Raman modes i n c r y s t a l s of TCNQ, TTF, K(TCNQ), CS~(TCNQ)~

perylene-TCNQ and phenazine-TCNQ, were o b t a i n e d i n a diamond c e l l i n t h e pres- s u r e range 0 t o 70 Kbar. The mode Gruneisen parameter were found t o span seve- r a l o r d e r s of magnitude. It i s concluded t h a t a l l of t h e observed low frequen- cy modes i n t h i s c l a s s of compounds a r e mixed modes of i n t e r n a l and e x t e r n a l c h a r a c t e r s .

The unusual p h y s i c a l p r o p e r t i e s of complexes i n v o l v i n g t h e molecules t e t r a - t h i a f u l v a l e n e (TTF) and

l a s t decade c o n s i d e r a b l e a c t i v i t y i n t h e f i e l d of o r g a n i c m a t e r i a l s r e s e a r c h . It h a s been customary t o d e s c r i b e t h e l a t t i c e dynamics of t h e s e compounds i n terms of i n t e r n a l modes and e x t e r n a l modes, w i t h t h o gap between t h e two regimes l y i n g b e t - ween 200 and 300 em-'. We have s t u d i e d t h e p r e s s u r e dependence of t h e phonons i n c r y s t a l s of TCNQO ,

K(TCNQ) , C s 2 (TCNQ) 3, perylene-TCNQ and phenazine-TCNQ i n o r d e r t o l e a r n about t h e i r bond a n h a r m o n i c i t i e s . The p r e s s u r e d a t a was ambiguous w i t h r e s p e c t t o t h e d i v i s i o n of t h e modes and we found it n e c e s s a r y t o perform g a s phase s p e c t r a . We found by h e a t i n g p u r i f i e d TCNQ powder i n a q u a r t z c e l l , gas phase v i b r a t i o n s a t 40, 76, 145, 340, 1225, 1454, 1606 and 2230 cm-I ( s e e Fig. 1 ) . The low frequency modes i n d i c a t e t h a t t h e gap between i n t e r n a l and e x t e r n a l modes l i e s below 40 cm-I.

The p r e s s u r e dependence of t h e c r y s t a l phonons f o r

a r e given i n Table 1.

The q u a n t i t y - - dv i s p r o p o r t i o n a l t o t h e mode Gruneisen parameter y ; t h e y v s

v

dp

frequency dependence f o r TCNQ' i s shown i n Fig. 2. The o t h e r compounds s t u d i e d r e - v e a l e d s i m i l a r p l o t s , i . e .

spans o v e r two o r d e r s of magnitude and i t d e c r e a s e s monotonically a s a f u n c t i o n of t h e frequency. F u r t h e r , d e t a i l s a r e a v a i l a b l e ( 1 ) .

sum mar^. - From t h e g a s phase Raman spectrum of

and from t h e mode Gruneisen parameter d i s t r i b u t i o n , no simple p i c t u r e of mode s e p a r a t i o n between e x t e r n a l and i n t e r n a l ones i n

can be d e r i v e d . S t a t e d o t h e r w i s e , t h e r e is no c l e a r c u t d i s - t i n c t i o n between s t r o n g i n t r a m o l e c u l a r and weak i n t e r m o l e c u l a r f o r c e s , b u t r a t h e r a continuous v a r i a t i o n of bond s t r e n g t h ever s e v e r a l o r d e r s of magnitude.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981694

JOURNAL DE PHYSIQUE

v

cm-'>

0 --

CO dp

'e ^{g a s} c r y s t a i (cm-'/kbar)

-

c

40 45 0.42

7 6 6 7 1.00

0

-

4

-

rr)

85 0.83

* - ^{106 1.97}

\ \ 14 5 144 0.64

154 0.56

0 10 ^{163 1.39}

pr)

180 1 . 7 8

300 0.25

340 330 0.34

0 0 ^{368 0.45}

to 427 0.25

590 0.08

712 0.36

0

- 1 0 - 751 0.06

t i

* 7 ^{950 0.39}

E ^{1189 0.78}

0

Y

1225 1206 0.42

- O h 0 1317 0.58

cu 1334 0.17

1445 0.53

1454 1456 0.50

- 0 _lfl - _{1606 1597 1602} ^0.48 _0.45

2228 0.42

2230 2232 0.39

- ₀ 0 - T a b l e 1.

Gas p h a s e v i b r a t i o n and c r y s t a l phonons i n TCNQO. The pressu- r e dependence of t h e phonons i s g i v e n . The q u a n t i t y 1 &,L i s p r o p o r t i o n a l

- 0 t o t h e mode Gruneisen parameter, and :: ^dp

10 i t i s p l o t t e d a s a f u n c t i o n of f r e - quency i n F i g . 2.

I ₀

0 0 0

0 0

Tf CU

FIG. 1

Raman i n t e n s i t y of TCNQ- g a s phase.

F i g . 2

P r e s s u r e dependence of t h e phonons i n

The q u a n t i t y dv i s p r o p o r t i o n a l t o t h e mode Grflneisen parameter. For c r y s t a l s having

y=,, -

one type oPPbond, such a s t h e 111-V t e t r a h e d r a l l y bonded semiconductors,y i s essen- t i a l l y c o n s t a n t . For c r y s t a l s having two t y p e s of bonds, such a s molecular c r y s t a l s and l a y e r s t r u c t u r e s , y assumes two v a l u e s , one corresponding t o low frequency modes and t h e o t h e r t o t h e high frequency modes. For t h e compounds s t u d i e d h e r e , TTFO, TCNQ', K(TCNQ), C S ~ ( T C N Q ) ~ , perylene-TCNQ and phenazine-TCNQ, y i s a monotonically d e c r e a s i n g f u n c t i o n of t h e frequency, covering s e v e r a l o r d e r s of magnitude.

References. -

1. C . Carlone, N.K. Hota,

S t o l z ,

E l b e r t ,

Kuzmany and H.D. Hochheimer. J.

Chem. Phys. t o appear Oct. 1981.