66 th OSU International symposium on molecular spectroscopy

66 th 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 F 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 Phosphates: (RO)3 P(O) TMP TEP organosulfide compounds DMSO SOCl 2 TBP Alkyl Phosphonates: (RO)2 P(O)R’ DMMP DEMa. P F 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

FTIR spectroscopy using the synchrotron radiation Interferometer Res. Max: 10 -3 cm-1 30 MHz Multipass cell : Max = 200 m Synchrotron beam entrance FImprovement 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) DMMP TEP MIR / (P=0. 03 mbar) NIR

FTIR spectra of DMMP, TMP and TEP using SOLEIL (Smirnova & al. J. Phys. Chem. B 2010, 114, 16936– 16947) THz Improvment of the S/N ratio Access to the THz torsional spectra Detection and analysis of the less volatile compounds FIR

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 TEP TMP FFor DMMP and TMP, MP 2 and B 3 LYP calculations confirm the coexistence of two lowest energy conformations C 1 & C 2 with almost similar populations FFor 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 (B 3 LYP/6 -311 G++(3 df, 2 pd)) TEP DEMa. P 53, 1 % 11, 6% 58, 4 % 22, 2 % 8, 9 % 7, 2 % 26, 1% 9, 2% 2, 2 % 1, 1 %

FIR Vibrational assignment of the FTIR spectra MIR NIR

Vibrational modes well suited for the conformational discrimination FThe 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: F In the MIR for specific P=O stretching modes F In the FIR for the most of non-localized modes

Vibrational and conformational analysis of the THz/FIR active modes FTheoretical vs experimental THz spectra FTheoretical vs experimental FIR spectra J Generally, the contributions of the different stable conformations may be isolated! J 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 FThe 11 and 23 modes correspond to the in plane and out of plane bending vibrations of the OSC 2 frame related respectively to the ‘parallel’ and ‘perpendicular’ bands JThe 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 ν 11 (Cuisset & al. Chemical Physics Letters 492 (2010) 30– 34) FCombining 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 ν 23 FCompared to ν 11 the P and R branches of the ν 23 band are very congested and may not be treated as an isolated band. FOnly in the Q branch, ΔKc=± 1 transitions show regular structures allowing to start a Loomis-Wood analysis. F We managed to model several p. Q and r. Q branches (ΔJ=0; ΔKc=± 1) multiplets well enough for picking combination frequencies and making unambiguous assignments.

High resolution analysis of the rovibrational spectrum of DMSO : the asymmetric band ν 23 Kc: 11← 10 Kc: 10← 9 Kc: 9← 8 FMore 400 ΔJ=0 ΔKc=± 1 transitions have been assigned at the experimental accuracy! FThe fit of the P and R branches is still in progress F Interactions with other vibrational states have to be taken into account for the complete assignment.

Next considered experiments FNext step in the organophosphorous study: Resolve the rotational pattern of DMMP and TMP at low temperature: n i S E L I A Jet LEIL SO FNext high resolution study of organosulfide compounds:

SOCl 2 : FIR ν , ν 2 3 4 & ν bands have been resolved in SOLEIL! 5 ν 3 ν 2 & ν 3 have been recorded at P=0. 05 mbar ν 4 & ν 5 have been recorded at P=0. 005 mbar ν 5 A more ambitious goal in the spectroscopic study of SOCl 2 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.

Thanks for your attention