66th OSU International symposium on molecular spectroscopy June 20 – 24 2011 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. Bocquet Laboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale, Dunkerque, France O. Pirali, P. Roy Advanced Infrared Lines Exploited for Spectroscopy, Synchrotron SOLEIL, Saint Aubin, France

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 compounds organophosphorous compounds Alkyl Phosphonates:(RO)2P(O)R’ Alkyl Phosphates:(RO)3P(O) DMMP DEMaP TBP TEP TMP organosulfide compounds DMSO SOCl2 Relatively non-toxic molecules characterized by functional groups common with real chemical warfare agents Yperite (mustard gas) Soman (nerve agent)

Low-resolution gas phase vibrational spectroscopy of organophosphorous compounds

Synchrotron beam entrance FTIR spectroscopy using the synchrotron radiation Interferometer Res. Max: 10-3 cm-1  30 MHz Multipass cell : Max = 200m Synchrotron beam entrance Improvement of the TEP detection at room temperature (L=150 m)

FTIR spectra of DMMP, TMP and TEP using thermal sources (Cuisset & al. J. Phys. Chem. B 112 (39), pp 12516 – 12525, (2008).) FIR (P=0.1 mbar) MIR / NIR (P=0.03 mbar) DMMP TMP TEP

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

Conformational analysis for larger organophosphorous compounds Determination of a complex conformational landscape using quantum chemistry calculations (B3LYP/6-311G++(3df,2pd)) TEP 58,4 % 22,2 % 8,9 % 7,2 % 2,2 % 1,1 % DEMaP 53,1 % 26,1% 11,6% 9,2%

Vibrational assignment of the FTIR spectra FIR MIR NIR

Vibrational modes well suited for the conformational discrimination 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 The large amplitude motions observed in the FIR show the largest frequency differences between conformers.

Vibrational and conformational analysis of the THz/FIR active modes Theoretical vs experimental FIR spectra Theoretical vs experimental THz 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 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 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

High resolution analysis of the rovibrational spectrum of 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 spectrum of 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 spectrum of DMSO : the asymmetric band ν23 Kc: 11←10 Kc: 10←9 Kc: 9←8 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.

Next high resolution study of organosulfide compounds: 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 mbar ν4 & ν5 have been recorded at P=0.005 mbar ν5 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.

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