GAS PHASE THZ SPECTROSCOPY OF ORGANOSULFIDE AND ORGANOPHOSPHOROUS COMPOUNDS USING A SYNCHROTRON SOURCE

A. Cuisset, I. Smirnova, G. Mouret , F. Hindle, C. Yang, S. Eliet, R. BocquetLaboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale,

Dunkerque, FranceO. Pirali, P. Roy

Advanced Infrared Lines Exploited for Spectroscopy, Synchrotron SOLEIL,

Saint Aubin, France

66th OSU International symposium on molecular spectroscopy

June 20 – 24 2011

organosulfide compounds

DMSO SOCl2

THz analysis of organosulphide and organophosphorous molecules: an example of toxic agent simulant compounds

Goal: French military agency (DGA) purposed us to demonstrate the ability of THz / FIR spectroscopy for the detection of toxic agents

simulant compoundsorganophosphorous compounds

Alkyl Phosphonates:(RO)2P(O)R’Alkyl Phosphates:(RO)3P(O)

DMMP DEMaPTBPTEPTMP

Relatively non-toxic molecules characterized byfunctional groups common with real chemical warfare agents

Yperite (mustard gas)Soman (nerve agent)

Low-resolution gas phase vibrational spectroscopy of

organophosphorous compounds

FTIR spectroscopy using the synchrotron radiation

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résolution 0.05 cm-1

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Rayonnement synchrotron

10 scans

résolution 0.5 cm-1

L=150 m

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Source interne glowbar

500 scans

résolution 0.5 cm-1

L= 20m

Improvement of the TEP detection at room temperature (L=150 m)

Multipass cell :

Max = 200m

Synchrotron beam entrance

Interferometer

Res. Max:

10-3 cm-1 30 MHz

FTIR spectra of DMMP, TMP and TEP using thermal sources(Cuisset & al. J. Phys. Chem. B 112 (39), pp 12516 – 12525, (2008).)

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SpectreIR TMP 0.0026 mbar 0.5 cm-1 50 scans

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DMMP

TMP

TEP

FIR (P=0.1 mbar)

MIR / NIR(P=0.03 mbar)

FTIR spectra of DMMP, TMP and TEP using SOLEIL(Smirnova & al. J. Phys. Chem. B 2010, 114, 16936–16947)

THz FIRImprovment of the S/N

ratio

Access to the THz torsional spectra

Detection and analysis of the less

volatile compounds

Theoretical analysis of the conformational landscape of alkyl phosphate and alkyl phosphonate compounds

Alkyl phosphate and alkyl phosphonate are very well known for their large conformational flexibility.

The vibrational assignment required to identify the lowest energy conformers

DMMP

TMP

For DMMP and TMP, MP2 and B3LYP calculations confirmthe coexistence of two lowest energy conformations C1 & C2

with almost similar populations

TEP

For TEP, the conformational landscape is very complex due to the increasing number of torsional axes.

Conformational analysis for larger organophosphorous compounds

DEMaP

53,1 % 26,1%

11,6% 9,2%

TEP

58,4 % 22,2 %

8,9 % 7,2 %

2,2 % 1,1 %

Determination of a complex conformational

landscape using quantum chemistry calculations

(B3LYP/6-311G++(3df,2pd))

Vibrational assignment of the FTIR spectraFIR MIR NIR

Vibrational modes well suited for the conformational discrimination

The large amplitude motions observed in the FIR show the largest frequency differences between

conformers.

6 & 7 modesof DMMP

Strong c-type 27 bandsof TMP

The experimental evidences of the coexistence of two low energy conformers for DMMP and TMP may be

performed: In the MIR for specific P=O stretching modes

In the FIR for the most of non-localized modes

Vibrational and conformational analysis of the THz/FIR active modes

Theoretical vs experimental THz spectra

Theoretical vs experimental FIR spectra

Generally, the contributions of the different stable conformations may be isolated! Except for the lowest frequency modes of the largest molecules, a very good agreement

is obtained between experimental and theoretical spectra.

High-resolution rovibrational

spectroscopy of organosulfide compounds

FIR high resolution rovibrational spectroscopy of DMSO

The rotational structure of the P, Q, R branches for the lowest frequency vibrational bands has been resolved (resolution: 1.5*10-3 cm-1 45 MHz)

Very long average time (800 scans 53 hours) in order to reach SNR > 100

The 11 and 23 modes correspond to the in plane and out of plane bending vibrations of the OSC2 frame related respectively to the ‘parallel’ and

‘perpendicular’ bands

High resolution analysis of the rovibrational spectrumof DMSO : the symmetric band ν11

(Cuisset & al. Chemical Physics Letters 492 (2010) 30–34)

Combining recent pure rotational transitions measured by Margulès et al. and our FIR measurements, we adjusted all parameters in H and we reproduced the experimental data

close to their experimental accuracy.

High resolution analysis of the rovibrational spectrumof DMSO : the asymmetric band ν23

Compared to ν11 the P and R branches of the ν23 band are very congested and may not be treated as an isolated band.

Only in the Q branch, ΔKc=±1 transitions show regular structures allowing to start a Loomis-Wood analysis.

We managed to model several pQ and rQ branches (ΔJ=0; ΔKc=±1) multiplets well enough for picking combination frequencies and making unambiguous assign- ments.

High resolution analysis of the rovibrational spectrumof DMSO : the asymmetric band ν23

More 400 ΔJ=0 ΔKc=±1 transitions have been assigned at the experimental accuracy! The fit of the P and R branches is still in progress Interactions with other vibrational states have to be taken into account for the complete assignment.

Kc: 11←10 Kc: 10←9 Kc: 9←8

Next considered experiments

Next step in the organophosphorous study: Resolve the rotational pattern

of DMMP and TMP at low temperature:

Next high resolution study of organosulfide compounds:

Jet-AILES in

SOLEIL

SOCl2 : FIR ν2 ,ν3 ,ν4 & ν5 bands have been resolved in SOLEIL!

ν2 & ν3 have been recorded at P=0.05

mbarν4 & ν5 have been

recorded at P=0.005 mbar

A more ambitious goal in the spectroscopic study of

SOCl2 is the global experimental reconstruction of the whole system of the vibrational states of this

molecule and of the corresponding vibrational

potential and dipole moment functions.

ν2 ν3

ν5

Thanks for your attention