8
Spectrochimica Acta Part A 60 (2004) 329–336 Spectroscopic studies of the molecular interactions in n-ethylamines and 2-nitropropane/n-ethylamine mixtures Cédric Gobin , Philippe Marteau, Jean-Pierre Petitet Laboratoire d’Ingénierie des Matériaux et des Hautes Pressions, CNRS, Institut Galilée, Université Paris XIII, avenue J.B. Clément, 93430 Villetaneuse, France Received 12 March 2003; received in revised form 12 May 2003; accepted 22 May 2003 Abstract New experimental results are reported on molecular interactions in the n-ethylamines and 2-nitropropane (2-NP)/n-ethylamine mixtures studied by Raman spectroscopy under pressure in a diamond anvil cell (0–50 GPa) and, at ambient pressure, by infrared spectroscopy. Modifications of the infrared spectra in 2-NP in presence of triethylamine (TEA) or diethylamine (DEA) have been observed at ambient pressure and interpreted as a specific molecular interaction. High-pressure fluorescence in the vicinity of the liquid–solid phase transition of the 2-NP/DEA and 2-NP/monoethylamine mixtures, is highlighted and discussed. © 2003 Elsevier B.V. All rights reserved. Keywords: High-pressure; Raman spectroscopy; Infrared spectroscopy; n-ethylamines 1. Introduction Liquid mixtures of nitric acid and nitrocompounds have several practical advantages as propellants but remain still unavailable because of their hazardeous behaviour. The present communication is a contribution to the study of the effect of adding amines on the behaviour of these mixtures [1,2] The spectroscopic measurements are applied to the monopropellant model 2-nitropropane (2-NP)/nitric acid. The reactivity of this mixture is known to depend on a redox mechanism between the strong oxydant donor (nitric acid) and the acceptor (nitrocompounds) [3]. Different studies [2,4] show that the control of the ratio donor–acceptor is expected to modify the reactivity of the mixture. As nitric acid is a strong oxydant, the sensitivity of the system can be enhanced by modifying the acceptor. We are then interested in the action of amines on the 2-NP chosen as a model of acceptor nitrocompound. Raman and infrared spectroscopy have been used as non-intrusive methods to perform a microscopic analy- Corresponding author. Tel.: +33-1-49-403647; fax:+33-1-49-403414. E-mail addresses: [email protected] (C. Gobin), [email protected] (P. Marteau), [email protected] (J.-P. Petitet). sis of the samples. High-pressure is used as a suitable thermodynamic variable to study the evolution of the molecular interactions in the mixtures without chemical decomposition. In a previous work [5], pure 2-NP has been studied in the liquid and solid state by high-pressure Raman spectroscopy and the peaks have been assigned (Table 1). Pure liquid tri- ethylamine (TEA) and diethylamine (DEA) have been stud- ied by high-pressure Raman spectroscopy and at ambient pressure by infrared spectroscopy and the peaks assigned [6]. Pure monoethylamine (MEA) has been only studied at ambient pressure by Raman spectroscopy and a few peaks have been assigned [7]. Tables 2–4 summarize these results and Fig. 1 shows the semi-developed formulas of all com- pounds. New results of Raman spectroscopic measurements in a diamond anvil cell (DAC) (0–50GPa) in the TEA, the DEA and in the 2-NP/TEA, 2-NP/DEA, 2-NP/MEA mixtures as well as infrared spectroscopy at ambient pressure in the 2-NP/TEA and 2-NP/DEA mixtures are presented. 2. Experimental method The 2-NP (96 wt.% purity) was from Fluka, the TEA (99.5 wt.% purity), the DEA (99 wt.% purity) and the 1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1386-1425(03)00230-0

Spectroscopic studies of the molecular interactions in n-ethylamines and 2-nitropropane/n-ethylamine mixtures

Embed Size (px)

Citation preview

Spectrochimica Acta Part A 60 (2004) 329–336

Spectroscopic studies of the molecular interactions inn-ethylaminesand 2-nitropropane/n-ethylamine mixtures

Cédric Gobin∗, Philippe Marteau, Jean-Pierre Petitet

Laboratoire d’Ingénierie des Matériaux et des Hautes Pressions, CNRS, Institut Galilée, Université Paris XIII,avenue J.B. Clément, 93430 Villetaneuse, France

Received 12 March 2003; received in revised form 12 May 2003; accepted 22 May 2003

Abstract

New experimental results are reported on molecular interactions in then-ethylamines and 2-nitropropane (2-NP)/n-ethylamine mixturesstudied by Raman spectroscopy under pressure in a diamond anvil cell (0–50 GPa) and, at ambient pressure, by infrared spectroscopy.Modifications of the infrared spectra in 2-NP in presence of triethylamine (TEA) or diethylamine (DEA) have been observed at ambientpressure and interpreted as a specific molecular interaction. High-pressure fluorescence in the vicinity of the liquid–solid phase transition ofthe 2-NP/DEA and 2-NP/monoethylamine mixtures, is highlighted and discussed.© 2003 Elsevier B.V. All rights reserved.

Keywords: High-pressure; Raman spectroscopy; Infrared spectroscopy;n-ethylamines

1. Introduction

Liquid mixtures of nitric acid and nitrocompounds haveseveral practical advantages as propellants but remain stillunavailable because of their hazardeous behaviour. Thepresent communication is a contribution to the study of theeffect of adding amines on the behaviour of these mixtures[1,2] The spectroscopic measurements are applied to themonopropellant model 2-nitropropane (2-NP)/nitric acid.The reactivity of this mixture is known to depend on a redoxmechanism between the strong oxydant donor (nitric acid)and the acceptor (nitrocompounds)[3]. Different studies[2,4] show that the control of the ratio donor–acceptor isexpected to modify the reactivity of the mixture. As nitricacid is a strong oxydant, the sensitivity of the system can beenhanced by modifying the acceptor. We are then interestedin the action of amines on the 2-NP chosen as a model ofacceptor nitrocompound.

Raman and infrared spectroscopy have been used asnon-intrusive methods to perform a microscopic analy-

∗ Corresponding author. Tel.:+33-1-49-403647;fax:+33-1-49-403414.

E-mail addresses: [email protected] (C. Gobin),[email protected] (P. Marteau), [email protected](J.-P. Petitet).

sis of the samples. High-pressure is used as a suitablethermodynamic variable to study the evolution of themolecular interactions in the mixtures without chemicaldecomposition.

In a previous work[5], pure 2-NP has been studied in theliquid and solid state by high-pressure Raman spectroscopyand the peaks have been assigned (Table 1). Pure liquid tri-ethylamine (TEA) and diethylamine (DEA) have been stud-ied by high-pressure Raman spectroscopy and at ambientpressure by infrared spectroscopy and the peaks assigned[6]. Pure monoethylamine (MEA) has been only studied atambient pressure by Raman spectroscopy and a few peakshave been assigned[7]. Tables 2–4summarize these resultsandFig. 1 shows the semi-developed formulas of all com-pounds.

New results of Raman spectroscopic measurements in adiamond anvil cell (DAC) (0–50GPa) in the TEA, the DEAand in the 2-NP/TEA, 2-NP/DEA, 2-NP/MEA mixtures aswell as infrared spectroscopy at ambient pressure in the2-NP/TEA and 2-NP/DEA mixtures are presented.

2. Experimental method

The 2-NP (≥96 wt.% purity) was from Fluka, the TEA(99.5 wt.% purity), the DEA (99 wt.% purity) and the

1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved.doi:10.1016/S1386-1425(03)00230-0

330 C. Gobin et al. / Spectrochimica Acta Part A 60 (2004) 329–336

Table 1Fundamental Raman modes (cm−1) of 2-NP

Description[5] C3H7NO2

liquidC3H7NO2

solid [10]

Not assigned 278 319Not assigned 319 361Not assigned 353 391Oscillation in the plane

of the molecule of theNO2 group

525 524

Symmetrical bending ofthe NO2 angle

622 579

Not assigned 714Stretching of the C–N bond 852 855Not assigned 902 906Not assigned 946Not assigned 962Stretching of the C–C bond 1102 1102Not assigned 1140 1164Not assigned 1181 1178Not assigned 1306 1308Symmetrical stretching

of the N–O bond1359 1361

Symmetrical bending ofthe CH2 angle

1400 1405

Not assigned 1429Asymmetrical bending of

the CH2 angle1447 1465

Not assigned 1467 1489Asymmetrical stretching

of the N–O bond1550 1539

Not assigned 2928Symmetrical stretching

of the C–H bond2950 2965

Asymmetrical stretchingof the C–H bond

2998 3019

MEA (99.5 wt.% purity) were from Merck-Prolabo. Thecompounds have been used without further purification.

High-pressures measurements have been performed in ahigh-pressure membrane type DAC[8]. The pressure wasmonitored by a pneumatic ram connected to a pressuregenerator through a high-pressure flexible capillary. Thepressure was measured by the frequency shift of the fluores-cence singlet (685.4 nm at 0.1 MPa) of SrB4O7:Sm2+ chipsset inside the high-pressure chamber[9]. An argon ion laser(514, 53 nm) delivered 20 mW power on the sample whichis low enough to avoid heating and modification of the sam-ple. The diameter and the thickness of the samples are 150and 80�m, respectively. Raman spectra have been obtainedin the backscattering configuration using a triple monochro-mator micro-RamanDILOR XY multichannel spectrometerequipped with a nitrogen cooled CCD detector Jobin Yvon.With slits of 150 microns, the spectral resolution was 5cm−1. For infrared measurements, the samples were con-tained within a polyethylene gasket, 9 or 140�m of thick,maintained between two windows of caesium iodure. Spec-tra have been obtained at room temperature using a Fouriertransform interferometer,BOMEM MI55, equipped with aGLOBAR source and a DTGS detector.

Fig. 1. Semi-developed formulas of the 2-NP, of the TEA, of the DEAand of the MEA.

3. Results

3.1. High-pressure Raman results

The liquid–solid phase transition of 2-NP at around1.5 GPa is characterized by a red frequency shift of the622 cm−1 line (NO2 symmetrical bending mode) and ofthe 1550 cm−1 line (NO2 asymmetrical stretching mode),49 and 19 cm−1, respectively. These results are in goodagreement with those previously published within the res-olution range of the multichannel spectrometer[10]. Thehigh-pressure Raman measurements on TEA have beenperformed up to 50 GPa at room temperature. No phasetransition has been observed on the whole pressure range.All the lines are shifted toward higher frequencies (Fig. 2)and the broadening of these lines is attributed to the pres-sure effect on molecular interactions between neighbouringmolecules of TEA. A similar behaviour is observed for

Fig. 2. Evolution of the different vibration modes of the TEA versuspressure at room temperature.

C. Gobin et al. / Spectrochimica Acta Part A 60 (2004) 329–336 331

Table 2Fundamental Raman modes (cm−1) of the TEA

Description Takeuchi et al.[6] This work

Asymmetrical bending in the plane of the C–H bond of the CH3 group or symmetrical bending in theplane of the C–H bond of the CH2 group

1455 1454

Symmetrical bending in the plane of the C–H bond of the CH3 group or asymmetrical bending out ofplane of the C–H bond of the CH2 group

1383 1380.7

Symmetrical bending in the plane of the C–H bond of the CH3 group or asymmetrical bending out ofplane of the C–H bond of the CH2 group

1371 1368.6

Symmetrical bending in the plane of the C–H bond of the CH3 group or asymmetrical bending out ofplane of the C–H bond of the CH2 group

1362 1360.2

Symmetrical bending out of plane of the C–H bond of the CH2 group 1314 1314.6Symmetrical bending out of plane of the C–H bond of the CH2 group 1294 1292.1Symmetrical bending out of plane of the C–H bond of the CH2 group 1272 1270Stretching of the C–N bond 1209 1210.2Asymmetrical bending in the plane of the C–H bond of the CH3 group 1144 1145.6Asymmetrical bending in the plane of the C–H bond of the CH3 group 1084 1082.9Asymmetrical bending in the plane of the C–H bond of the CH3 group or stretching of the C–C bond 1068 1065.7Stretching of the C–C bond 1048 1046.2Stretching of the C–C bond 1021 1019.6Asymmetrical bending in the plane of the C–H bond of the CH3 group or stretching of the C–C bond 998 997.6Asymmetrical bending in the plane of the C–H bond of the CH3 group or stretching of the C–C bond 920 919.2Asymmetrical bending in the plane of the C–H bond of the CH3 group or stretching of the C–C bond 909 Not observedAsymmetrical bending in the plane of the C–H bond of the CH2 group or asymmetrical bending in the

plane of the C–H bond of the CH3 group813 811.7

Asymmetrical bending in the plane of the C–H bond of the CH2 group or asymmetrical bending in theplane of the C–H bond of the CH3 group

801 802

Stretching of the C–N bond 740 742.5Stretching of the C–N bond 736 735.1Bending of the NCC angle 536 533.2Bending of the NCC angle or bending of the CNC angle 492 Not observedNot assigned 463 461.3Bending of the CNC angle 439 437.8Bending of the NCC angle or bending of the CNC angle 428 426.8Bending of the NCC angle 340 338.7Bending of the NCC angle or bending out of plane of the methyl group 296 291.7

DEA (Fig. 3). However, the broadening of the lines are stillmore significant.

The 2-NP/TEA (15 mol.%), 2-NP/DEA (15 mol.%) and2-NP/MEA (15 mol.%), have been studied at room tempera-ture in the 0–15 GPa pressure range. No interaction betweenthe 2-NP and either of the threen-ethylamines is observedat ambient pressure and the spectra of the mixtures are the

Fig. 3. Evolution of the different vibration modes of the DEA versuspressure at room temperature.

simple superposition of the spectra of the pure products. Theliquid–solid phase transition of 2-NP in the 2-NP/TEA (15mol.%) mixture is located at around 2 GPa and shows a redshift of the NO2 symmetrical bending mode (43.5 cm−1)

Fig. 4. Evolution of asymmetrical bending mode of the N–O bond of2-NP at around the liquid-phase transition of 2-NP in the pure 2-NP andin the 2-NP/TEA mixtures versus pressure at room temperature.

332 C. Gobin et al. / Spectrochimica Acta Part A 60 (2004) 329–336

Table 3Fundamental Raman modes (cm−1) of the DEA

Description Takeuchi et al.[6] This work

Stretching of the N–H bond 3315 3316.7Asymmetrical stretching bonds C–H of the CH3 group 2965 2968.7Asymmetrical stretching bonds C–H of the CH2 group 2926 2924.7Symmetrical stretching bonds C–H of the CH3 group 2887 2889.7Symmetrical stretching bonds C–H of the CH2 group 2865 2871.8Asymmetrical bending in the plane of the C–H bond of the CH3 group or symmetrical bending in the

plane of the C–H bond of the CH2 group1479 1482.2

Asymmetrical bending in the plane of the C–H bond of the CH3 group 1452 1454.8Asymmetrical bending in the plane of the C–H bond of the CH3 group or symmetrical bending in the

plane of the C–H bond of the CH2 group1432 ?

Symmetrical bending in the plane of the C–H bond of the CH3 group 1382 1380.7Symmetrical bending out of plane of the C–H bond of the CH2 group 1358 1361.9Asymmetrical bending out of plane of the C–H bond of the CH2 group or symmetrical bending in the

plane of the C–H bond of the CH2 group or symmetrical bending out of plane of the C–H bond ofthe CH2 group

1324 1326.3

Asymmetrical bending out of plane of the C–H bond of the CH2 group or symmetrical bending out ofplane of the C–H bond of the CH2 group

1284 1286.8

Asymmetrical bending out of plane of the C–H bond of the CH2 group 1254 1256.3Asymmetrical bending in the plane of the C–H bond of the CH3 group or asymmetrical bending in the

plane of the C–H bond of the CH2 group1193 1194.9

Asymmetrical bending in the plane of the C–H bond of the CH3 group 1135 1138.7Stretching of the C–C bond or stretching of the C–N bond 1092 1096.1Asymmetrical bending in the plane of the C–H bond of the CH3 group or stretching of the C–N bond 1063 1065.7Stretching of the C–N bond or stretching of the C–C bond 1043 1045.4Asymmetrical bending in the plane of the C–H bond of the CH3 group or stretching of the C–C bond 1034 1034.5Asymmetrical bending in the plane of the C–H bond of the CH3 group or stretching of the C–C bond or

asymmetrical bending out of plane of the C–H bond of the CH2 group1020 1021.93

Asymmetrical bending in the plane of the C–H bond of the CH3 group or stretching of the C–C bond orstretching of the C–N bond

925 924.8

Asymmetrical bending in the plane of the C–H bond of the CH2 group or asymmetrical bending in theplane of the C–H bond of the CH3 group

886 886.6

Stretching of the C–N bond or asymmetrical bending in the plane of the C–H bond of the CH2 group 864 865.8Stretching of the C–C bond or asymmetrical bending in the plane of the C–H bond of the CH2 group or

asymmetrical bending in the plane of the C–H bond of the CH3 group820 820

Stretching of the C–N bond 777 778.8Stretching of the C–N bond or bending of the CNC angle or asymmetrical bending in the plane of the

C–H bond of the CH2 group or bending of the CNH angle727 727.6

Bending of the CNH angle 495 494.8Bending of the CNH angle 425 425.15Bending of the CNH angle or stretching of the C–C bond 369 368.5Bending out of plane of the methyl group or bending of the CNC angle or bending of the CNH angle 300 297.7Bending out of plane of the methyl group or bending of the CNH angle 246 NVBending of the CNC angle or bending out of plane of the ethyl group 130 NV

and of the NO2 asymmetrical stretching mode (12 cm−1).A pressure induced fluorescence occurs in 2-NP/DEA (15mol.%) which increases up to the liquid–solid phase transi-tion located at around 1.5 GPa. This transition shows a redshift of the NO2 asymmetrical stretching mode (17 cm−1).The fluorescence is less important in the solid phase but

Table 4Fundamental Raman modes (cm−1) of the MEA

Description Dollish et al.[7] This work

Asymmetrical stretching of the N–H bond 3371 3368Symmetrical stretching of the N–H bond 3318 3319Symmetrical bending of the N–H bond 1619 1602Stretching of the C–N bond 1085 1084

does not disappear and seems to be independent of the pres-sure. At around 0.5 GPa, fluorescence also appears in the2-NP/MEA (15 mol.%) mixture and masks all the peaks.In this case fluorescence does not disappear in the wholepressure range. A part of these results are shown onFig. 4.

3.2. Ambient pressure infrared measurements

2-NP/TEA and 2-NP/DEA mixtures, containing 5, 10, 15,30 and 50 mol.% of TEA and DEA, respectively have beenstudied by infrared spectroscopy at room temperature. Theexperimental spectra of these mixtures have been comparedwith the spectra expected from the addition of the spectra ofthe pure components after these spectra have been weighedto take into account the respective concentration.Fig. 5a–eshow that built spectra agree with the experimental ones ex-

C. Gobin et al. / Spectrochimica Acta Part A 60 (2004) 329–336 333

Fig. 5. (a), (b), (c), (d) and (e) Comparison of the experimental spectra (in bold) and synthetic spectra in the 2-NP/TEA mixtures composed, respectivelyof 5, 10, 15, 30 and 50% (mol/mol) of TEA.

cept for the peak at 1550 cm−1 of 2-NP/TEA (asymmetricalbending mode of the NO2), which is strongly greater in theexperimental spectra than in the calculated ones.Fig. 6a–eshow that the same 1550 cm−1 peak is exalted in presenceof DEA. Graph 1shows that the FWHM of this bond de-creases similarly with the concentrations of TEA and DEA.Moreover,Fig. 7 shows the appearance of a new peak sit-uated at 3318 cm–1 in the 2-NP/DEA mixture whereas theexpected peak of DEA at 3280 cm−1 (N–H stretching) is notobserved for weak concentrations in DEA.Graph 2, report-ing the ratio of the peak at 3318 cm−1 on the peak at 3280cm−1, shows a less increase of the peak at 3318 cm−1 thanthe one at 3280 cm−1. Fig. 8 shows the shift of the 3318

cm−1 peak of DEA diluted in benzene (for the curves a andb the thick of the sample was 140�m and for the curve (c),it was 2 mm). This proves the existence of hydrogen bondsin the pur DEA. Similarly,Fig. 9 shows that the 727 cm−1

peak of the pure DEA appears at around 750 cm−1 for lowconcentrations of DEA and shifts toward the lower frequen-cies when the concentration increases.

4. Discussion

These results show that the presence ofn-ethylaminesmodifies the molecular environment of 2-NP. The decrease

334 C. Gobin et al. / Spectrochimica Acta Part A 60 (2004) 329–336

Fig. 6. (a), (b), (c), (d) and (e) Comparison of experimental spectra (in bold) and synthetic spectra in the 2-NP/DEA mixtures composed, respectivelyof5, 10, 15, 30 and 50% (mol/mol) of DEA.

of the FWHM of the 1550 cm−1 line (asymmetrical bend-ing mode of the NO2 in 2-NP) shows that the addition ofamine reduces the molecular interactions between the 2-NPmolecules. Wolff et al.[11] have studied solutions of DEA inn-hexane and in carbon tetrachloride. They observed that the3280 cm−1 line (N–H stretching) is absent at high dilutionand increases with the increase of amine concentration. Theyconcluded that the presence of a line at 3320–3340 cm−1 be-longs to the free NH groups. We did the same observationsfor the 2-NP/DEA mixture (Figs. 7–9). So, in this mixture,

some of the DEA molecules seem to be bonded to them-selves and some of them seem to be free. The large frequencyshift of the 727 cm−1 line of the DEA toward the higher fre-quencies (23 cm−1), observed in the 2-NP/DEA mixtures,seems to go in the same way (Figs. 7–9). The decrease of theFWHM of the 1550 cm−1 line in the 2-NP/amine mixtureshaving the same proportions for the TEA and the DEA, itseems that the associated DEA molecules and the free DEAmolecules interact similarly with the 2-NP molecules. Thisseems to indicate too that hydrogen bonds, present in the

C. Gobin et al. / Spectrochimica Acta Part A 60 (2004) 329–336 335

Graph 1. Evolution of the FWHM the peak situated at 1548 cm−1 infunction of the percent of TEA and of DEA in the 2-NP/TEA and2-NP/DEA mixtures.

Fig. 7. Infrared spectra of the 2-NP/DEA mixtures composed, respectivelyof 0 (a), 5 (b), 10 (c), 15 (d), 30 (e) and 50 (f) % (mol/mol) of DEAand infrared spectra of the pure DEA (g).

pure 2-NP, are partially shared with the doublet of the ni-trogen atom. Jinshan and Heming[12] and Ishida[13] haveobserved, by molecular orbital calculations, that the inter-molecular interactions affect slightly the strength of C–NO2

Graph 2. Ratio of the intensities of the peaks at 3280 and 3320 cm−1 ofthe DEA in the 2-NP/DEA mixture.

Fig. 8. Evolution of the peak corresponding to the bending mode of theN–H bond of the DEA in function of the percent (in volume) of the DEAin benzene: (a) 1% (b) 3% and (c) 33%.

bonds of nitromethane and TNB (1,3,5-Trinitrobenzene) inmixtures containing the C–NO2 and NH2 groups, and thatthe protonation of the alkylamines extends the C–N bond.However, no shift of the peak corresponding to the stretchingmode of the C–N bond of the 2-NP or the amine has beenobserved. Taking into account that in the same conditionsany change of the Raman spectra (then no modification ofthe charge transfer in the mixture) has ever been observed,these features indicates rather the formation in the mixtureof a complex between the amine and the 2-NP.

On the other hand, the occurring of fluorescence aroundthe high-pressure liquid–solid phase transition of 2-NP/DEAand 2-NP/MEA is correlate with the presence of hydrogen inthe amines. This lets to suppose that a pressure formation ofhydrogen bonds in the mixture induces a disordering of themixture responsible for this fluorescence. It is worthwhile toremark that the fluorescence pressure range is more higherfor MEA than DEA mixtures, and corresponds to a doublingof the hydrogen’s number in MEA.

Fig. 9. Infrared spectra of the 2-NP/DEA mixtures composed, respectivelyof 5 (a), 10 (b), 15(c), 30 (d) and 50 (e) % (mol/mol) of DEA, of thepure DEA (f) and of the pure 2-NP (g).

336 C. Gobin et al. / Spectrochimica Acta Part A 60 (2004) 329–336

5. Conclusion

(1) The presence of DEA and TEA in 2-NP involves amodification of the intermolecular interactions in 2-NP; (2)at ambient pressure, the amine/2-NP mixture favours the for-mation of a complex staking the doublet of the amine’s nitro-gen atom (3) under pressure, a phenomenon of fluorescenceappears in the 2-NP/amine mixtures when the amine carriesa hydrogen atom on its nitrogen atom (DEA and MEA). Thissupposes that the high-pressure induces on the low-pressurecomplex, a redistribution of the hydrogen bonds between theneighbouring molecules. Larger is fluorescence range morehigh is the number of hydrogen atoms, carried by the nitro-gen of the amine. The 2-NP/TEA mixture does not presentany fluorescence under pressure.

Acknowledgements

The CEA Le Ripault, France is gratefully acknowledgedfor its financial support.

References

[1] C.P. Constantinou, T. Mukunkan, M.M. Chaudhri, Philos. Trans. R.Soc. 339 (1992) 403.

[2] H. Lucas, J.-P. Petitet, Propell. Explos. Pyrot. 27 (2002) 217.[3] J. Quinchon, Poudres, propergols et explosifs 1, Lavoisier,

1984.[4] P. Claude, Contribution à l’étude de la détonation des mélanges acide

nitrique-nitropropane, Poitiers, Université de Poitiers, 1965.[5] G. Geiseler, H. Kessler, J. Fruwert, Ber. Bunsenges. Physik. Chem.

70 (1966) 918.[6] H. Takeuchi, T. Kojima, T. Egawa, S. Konaka, J. Phys. Chem. 96

(1992) 4389.[7] F.R. Dollish, W.G. Fateley, F.F. Bentley, Characteristic Raman Fre-

quencies of Organic Compounds, Wiley, New York, 1974.[8] R. Letoullec, J.P. Pinceaux, P. Loubeyre, High Pressure Res. 1 (1988)

77.[9] A. Lacam, C. Chateau, J. Appl. Phys. 66 (1989) 366.

[10] H. Lucas, J.-P. Petitet, Phys. Chem. A. 103 (1999) 8952.[11] H. Wolff, G. Gamer, Spectrochim. Acta 28A (1972) 2121.[12] L. Jinshan, X. Heming, Propell. Explos. Pyrot. 25 (2000) 26.[13] H.Z. Ishida, Naturforsch 55a (2000) 769.