Arnaud Cuisset, G. Mouret , R. Bocquet, F. HindleLaboratoire de Physico-Chimie de lAtmosphere, Universit du Littoral Cte dOpale, Dunkerque, FranceOlivier Pirali, Pascale RoyAILES beamline of the synchrotron SOLEIL, Saint-Aubin, FranceJean DemaisonLaboratoire de Physique des Lasers, Atomes & Molcules,Universit des Sciences et Technologies, Lille, France

Gas phase spectroscopy of organophosphorous compounds in a context of toxical agent simili analyis Context of the project: To demonstrate the ability of THz/FIR spectroscopy for the detection of chemical-warfare agents simili, especially in realistic conditions.Interest:

Defense : Alkyl phosphonates as simili of Nerve Agents as Sarin CH3P(O)(F)OCH(CH3)2 , Soman CH3P(O)(F)OCH(CH3)C4H9 , Tabun CNP(O) (CH3)2NC2H5O) Biologic: Alkyl phosphates are well known for their mutagenic and pathogenic activities Industry: Organic solvents, pesticides, hydraulic fluids, nuclear activity tracers Atmospheric: Organophosphorous react with atmospheric radicals as OH, NO3

Previous spectroscopic studies:

Jet-cooled FTMW spectroscopy on alkyl phosphonates and nerve agents in surety laboratories OTD NIST group, Gaithersburg, USA (DMMP:Suenram et al.,J. Mol. Spectrosc. 2002, 211, 110. DEMP, DEEP & DIMP: Da Bell et al., J. Mol. Spectrosc. 2004, 228, 230. ) Low-resolution vibrational spectroscopy in rare gas matrices on alkyl phosphates (TMP, TEP) TMP: Reva et al. Chem. Phys. Lett. 2005, 406, 126. , TEP: Vidya et al. J. Mol. Struct. 1999, 476, 97.

These studies were supplemented by quantum chemistry calculations in order to describe the conformational landscape of these highly flexible molecules.

Preliminary experiments :Four molecules selected for gas phase vibrational spectroscopy

First experimental results, FTIR spectroscopy of DMMP, TMP and TEP(collaboration with the team of the AILES beamline of the SOLEIL synchrotron) As preliminary experiments, we used the internal sources of the FTIR spectrometer to record the vibrational spectra of DMMP, TMP, TEP and TBP

MIR - NIR spectra 600 cm-1 5000 cm-1,(Globar sourceZnSe windows, MCT detection)FIR spectra 50 cm-1 650 cm-1(Mercury lampPTFE windowsSi Bolometer) Thanks to a multipass cell allowing an optical path of 20 m., the vibrational spectra of DMMP, TMP and TEP have been recorded using the room vapour pressure of the compounds.

For TBP, this room vapour pressure was insufficient for its detection.

MIR & FIR spectra have been recorded with a resolution of 0.5 cm-1 (50 interferograms averaged)

FTIR spectra of DMMP, TMP and TEPDMMPTMPTEPFIR (P=0.1 mbar)MIR / NIR(P=0.03 mbar)

Theoretical analysis of the conformational landscape of alkyl phosphate and alkyl phosphonate compoundsAlkyl phosphate and alkyl phosphonate are very well known for their large conformational flexibility. The vibrational assignment required to identify the lowest energy conformers

Vibrational assignment of the FTIR spectra

FIRMIR NIR

Comparison of the different levels of computation:

Three levels of computation of Gaussian 03 have been used and allowed to assign all the vibrational bands of DMMP (white) and TMP (black) with relative uncertainties lower than 5%: MP2/6-311++G(d,p) : circlesHarmonic B3LYP/6-311++G(d,p) with extension to (3df,2pd) for the P atom : squares Anharmonic B3LYP/6-311++G(d,p) with extension to (3df,2pd) for the P atom : triangles

The DFT calculation including the anharmonic force field contribution gives the best prediction in the MIR-NIR spectral regions but not for the lowest frequency modes in the FIR region!

Vibrational modes well suited for the conformational discrimination

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

Next experiments