The infrared dielectric function of liquid triethylamine

ELSEVIER

Journal of Molecular

THE INFRARED

Liquids67

(1995) 21 l-216

DIELECTRIC FUNCTION TRIETHYLAMINE*

OF LIQUID

J. P. Hawranek and W. Wrzeszcz

institute of Chemistry Uniwersity of Wrociaw XI-383 WROCLAW, F. Joliot-Curie 14, Poland

Abstract The spectra of both components

of the complex

refractive

index and of the

complex electric permittivity for liquid biethylamine at 298 K were estimated from thin film transmission spectra in the 3200 - 650 cm-’ range. From these data, the molar vibrational polarization was determined m selected regions, and their contribution to the total value for the studied molecule was discussed.

The spectra of both components

of the complex

polarizability of the molecule in liquid phase were also obtained in the studied region and discussed.

Introduction Triethylamine spectroscopic

(TEA) is an important and frequently

[1,2 and references

used proton

acceptor

in

cited therein] and dielectric [3] studies of hydrogen

bonded systems. It has found also a variety of numerous

other applications

sciences and technology. Despite of that, the basic spectroscopic

in chemical

data and physico-chemical

properties of neat liquid TEA are surprisingly poorly explored. The aim of this work was to obtain information on dielectric properties of liquid TEA in the Mid-Intiared

* This work is dedicated to Professor P. Huyskens. 0167-7322/95/$09.50 0 1995 Elwier SSDI 0167.7322 (95) 008764

Science B.V. All rights reserved

region.

212

Experimental and data processing In a previous work the thin film transmission

spectra in the 3200 - 650 cm-’

region and the integrated intensities were obtained experimentally and discussed [4]. In this work we extend the study by determining the spectra of both components

of the complex

refractive index: ri(o)=n(u)+ik(u)

using the procedure

(1)

described in more detail elsewhere [5] Subsequently, the spectra of

both components of the complex electric permittivity:

Z(0) = &‘( 0) + i&“( u)

(2)

were obtained in the entire studied region following Maxwell’s relations. All results were obtained at controlled temperature

of 298 K; u denotes wavenumbers

[cm-‘] throughout

this work.

Results and discussion Ihe dielectric jhction

In Fig.

1 the

i(u)

spectrum

3200 - 2400 cm-’ region

is shown.

stretching vibrations of the

-CH,

of the

studied

In this region,

and

> CH,

liquid triethylamine

in the

the bands corresponding

to the

groups are dominating. In general, 14

bands were identified in this region, out of which 8 were quantitatively described [4] in terms of band positions, half-widths and integrated intensities In particular, asymmetric stretching

the

2971.0 cm-’ and

modes of the -CH,

2933.4 cm-’ bands

correspond

and > CH, groups, respectively,

2873.3 cm-’ and 2804.9 cm-’ bands are related to the corresponding

to the while the

symmetric stretching

vibrations of these groups [4]. In Fig. 2 the second prominent TEA is presented.

In this region

absorption region

absorption

bands

(2400 - 650 cm-‘) of liquid

corresponding

to the numerous

deformation modes of the -CH, and > CH, groups occur, as well as of the C-C and C-N stretching modes. In this region 36 bands were quantitatively described [4].

213

0.0 3200

E”(V) 3100

3000

2300

2700

2800

2400

2500

2600

v

WI

Fig. 1. The i(u) spectrum of liquid triethylamine in the 3200 - 2400 cm“ region.

“1

0.30-

025.

1

TRIETHYLAMINE

020. 0.15. 0.10. 0.05. O.Oh 2400

P(V) 22On

2000

IS00

1600

1400

1200

1000

BOO vlcd

Fig. 2. The g(u) spectrum of liquid triethylamine in the 2400 - 650 cm“ retion.

214

As can be seen, several bands of TEA are intrinsically of medium strength, with the strongest asym-

v,(CH,)

at 2971 .O cm-’ showing EE

at the level of 0.1-0.2 as concerns

above 0.4; several other bands are

&;a

The molar vibrational polarization.

Using the dielectric function

i(v),

the molar vibrational polarization

determined for selected groups of vibrations (corresponding

P”

was

to related spectral ranges), with

the use of the procedure described elsewhere [6]. Because of the considerable overlapping of bands and difficulties with their exact assignement,

we did not attempt at this stage to

obtain values for particular modes. The results are presented in Table 1. Table 1. Molar vibrational polarization of liquid triethylamine in the M d-IR T=298 K. P Mb

Range [ cm-’]

AS’. 10’

[ cm3 .mole-’ ]

3200 - 2400

6.98 + 0.26

0.250 + 0.010

2400 - 650

24.66 k 0.30

0.869 If:0.010 1.119f0.010

CP”” 3200-

650

The values of P*

31.63 kO.18

1.131 +0.015

were calculated assuming a density value of 0.7235 g . cm-’ for

TEA at 298 K, which amounts to a molar volume of 139.86 cm-' .mole-' As can be seen, the overall value of the vibrational polarization of TEA related to modes exhibiting bands in the Mid-IR is not too impressive and amounts to only 1.12 cm.mole-’

It is interesting to

note, that the value related roughly to the CH stretching vibrations (i.e. corresponding the

3200 - 2400 cm-’ range)

is much smaller than that one corresponding

to

to the

deformation modes. The wavenumber dependent complex molecular polarizability

From 2(v) , the complex molecular polarizability function, with the assumption of the Lorentz internal field:

ir( v) , was calculated

215

&(o)=a’(u)+ia”(U)

Using the Clausius-Mossotti

(3)

equation in the form [7]:

$0)-l

A4

i(v)+2

d

--=

4

_tiA&(V)

(4)

3

one can obtain, by separation of the real and imaginary parts of ix(v) :

3 a’(v) = 4d,

&‘2(D)+&“*(LJ)+&‘(u)-22 [&‘(D)+2]t+&“*(u)

&‘I(0) 9 a”(U) = 4ldv, [&I(D)+2]* +P(v)

(5)

m

(6)

VI

were N, denotes Avogadro’s number and V,,, - the molar volume of the liquid. The shape of this spectrum for liquid TEA in the entire

studied

region is shown in Fig.3,

showing the relative intensities of all bands in a common scale.

a”‘@9 2000

1500

loo0

&m-l]

Fig. 3. The spectrum of the complex polarizability of liquid triethylamine, in units of

[ 1O-*’cm’ I molecule ]

216

At the high wavenumber limit of the spectrum, the level of a’(u) electronic polarizability of the molecule. With decreasing

is predetermined

wavenumbers,

by the

the vibrational

contributions become visible. The molar refraction

With the density value of 0.7235 g. cm-’ and the refractive index of 1.39697 (both at 298 K) the molar refraction of TEA amounts to 33.68 cm .moZe-’

Conclusion The total distortion polarization study equals to 34.80 cm.moK’

of the studied triethylamine

determined

in this

Thus, the vibrational contribution, stemming from modes

in the 3200 - 650 cm-’ range is very small, amounting to only ca. 3.2 %. This figure will obviously increase after the completion of the study with FIR data. This paper has been presented on the Molecular Spectroscopy

Conference [S]

References R. Kramer and G. Zundel, J. Chem. Sot. Faraday TransZZ 86 (1990) 301. S.E. Odinokov, V.P. Glazunov, A.A. Nabiullin, .JChem.Soc. Faraday Trans. II 80 (1984) 899. H. Ratajczak and L. Sobczyk, J. Chem. Phys. 50 (1969) 556; Bull. Acad. Pol. Sci., ser. xi chim. 18 (1970) 93. J.P. Hawranek, W. Wrzeszcz, and G.C Wycisk, Bull. Pal. Acad. SCI. (Chem.), 42 (1994) 141. J.P. Hawranek, W. Wrzeszcz and M. A. Czamecki, J. Mol. Strut.,

321 (1994) 13 1.

J.P. Hawranek and M. A. Czamecki, Chem. Phys. Letters, 151 (1988) 340. C.J.F. Bottcher and P. Bordewijk, Theov of Electric Polarization, Vol. II, Dielectrics in time-dependent fields, Ch. XII, Elsevier, Amsterdam 1978. J.P. Hawranek and W. Wrzeszcz, II-nd National Conference on Molecular Spectroscopy with International Participation, Wroclaw 27-30. IX. 1993. Book of Abstracts, P-22.