1. 66th OSU International symposium on molecular spectroscopy
June 20 –
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

2. 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)

3. Low-resolution gas phase vibrational spectroscopy of organophosphorous compounds

4. 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)

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

6. 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

7. 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.

8. 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%

9. Vibrational assignment of the FTIR spectra
FIR
MIR NIR

10. 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.

11. 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.

12. High-resolution rovibrational spectroscopy of organosulfide compounds

13. 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

14. 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.

15. 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.

16. 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.

17. 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

18. 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.

19. Thanks for your attention