Arnaud Cuisset, G. Mouret, R. Bocquet, F. Hindle Laboratoire de Physico-Chimie de l’Atmosphere, Université du Littoral Côte d’Opale, Dunkerque, France Olivier Pirali, Pascale Roy AILES beamline of the synchrotron SOLEIL, Saint-Aubin, France Jean Demaison Laboratoire de Physique des Lasers, Atomes & Molécules, Université 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. organophosphorous compounds Alkyl Phosphonates ((RO) 2 P(O)R) DMMP, (CH 3 O) 2 P(O)CH 3 DMEP, (CH 3 O) 2 P(O)C 2 H 5 DEEP, (C 2 H 5 O) 2 P(O)C 2 H 5 Alkyl Phosphates ((RO) 3 P(O)) TMP, (CH 3 O) 3 P(O) TEP, (C 2 H 5 O) 3 P(O) TBP, (C 4 H 9 O) 3 P(O) Interest:  Defense :  Alkyl phosphonates as simili of Nerve Agents as Sarin CH 3 P(O)(F)OCH(CH 3 ) 2, Soman CH 3 P(O)(F)OCH(CH 3 )C 4 H 9, Tabun CNP(O) (CH 3 ) 2 NC 2 H 5 O)  Biologic: Alkyl phosphates are well known for their mutagenic and pathogenic activities Industry: Organic solvents, pesticides, hydraulic fluids, nuclear activity tracers …  Industry: Organic solvents, pesticides, hydraulic fluids, nuclear activity tracers …  Atmospheric: Organophosphorous react with atmospheric radicals as OH, NO 3 … 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.  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. ) 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 DMMPTMPTEPTBP  All these molecules are liquid in standard conditions of temperature and pressure.  Their analysis in gas phase required to detect their vapour pressure at room temperature Measurements of vapour pressures from room to ebullition temperature were performed with the CCM Dunkirk using the static HS GC method:  At room temperature, more than 0.5 mbar are available for DMMP, TMP and TEP.  The ambient vapour pressure of TBP is lower than mbar.  For TBP, a vapour pressure of 0.5 mbar may be reached by increasing of the temperature to 90 °C

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 source ZnSe windows, MCT detection) FIR spectra 50 cm -1 – 650 cm -1 (Mercury lamp PTFE windows Si 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 TEP DMMP TMP TEP FIR (P=0.1 mbar) MIR / NIR (P=0.03 mbar)

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 confirm the 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. Vidya et al predicted 9 conformers with energy differences lower than 800 cm -1.  Here, we considered only the lowest energy conformer predicted with the B3LYP method with a C3 symmetry predicted with the B3LYP method with a C3 symmetry

Vibrational assignment of the FTIR spectra FIR MIR 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/ G(d,p) : circles Harmonic B3LYP/ G(d,p) with extension to (3df,2pd) for the P atom : squares Anharmonic B3LYP/ 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. 6 & 7 modes of DMMP Strong c-type 27 bands of 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

Conclusions  The gas phase vibrational spectra of DMMP, TMP and TEP have been recorded at room temperature using the IFS 125 spectrometer and fully assigned thanks to high level of theory computational methods.  At room temperature, the vapour pressure of TBP is too weak for its detection in the present experimental conditions  For DMMP and TMP, the coexistence of two low energy conformers have been evidenced both in the MIR and in the FIR regions  The anharmonic calculations are not suited to the prediction of the lowest frequency modes  The largest frequency differences between conformers are observed in this region Specificities of the FIR domain

Next experiments Advances Infrared Line Exploited for Spectroscopy  Short term: FT FIR spectroscopy using the AILES beam line of the SOLEIL synchrotron  To resume the previous experiments benefiting the best resolution the IFS 125 (< cm -1 ) to improve:  The resolution of the rotational patterns  The conformational discrimination  To detect TBP with an heated cell or at room T° with a longer optical path up to 100m. Two main goals  Middle term: THz-TDS and CW-THz spectroscopy using the optoelectronic THz sources THz TDS → Broad band ( 3 cm -1 – 150 cm -1 ) and low resolution (0.1 cm -1 ) technique  Study in solid phase of organophosphorous compounds (preparation of mixture: molecule – HDPE matrix) CW THz Spectroscopy → Tunable ( 3 cm -1 – 100 cm -1 ) and high spectral purity ( cm -1 )  Detection of rotational transitions in lowest energy excited vibrational states  Middle – Long term: Molecular beam spectroscopy for the larger alkyl phosphates and alkyl phosphonates  To simplify the conformational landscape of these molecules