THE JETCOOLED HIGHRESOLUTION FARIR SPECTRUM OF FORMIC ACID

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THE JET-COOLED HIGH-RESOLUTION FAR-IR SPECTRUM OF FORMIC ACID CYCLIC DIMER Sabath Bteich, Manuel Goubet,

THE JET-COOLED HIGH-RESOLUTION FAR-IR SPECTRUM OF FORMIC ACID CYCLIC DIMER Sabath Bteich, Manuel Goubet, Thérèse R. Huet, University of Lille/CNRS Olivier Pirali, CNRS/University Paris-Sud Pascale Soulard, Pierre Asselin, CNRS/University Pierre et Marie Curie Robert Georges, University of Rennes/CNRS ISMS – Urbana-Champaign (USA), June 18 -22, 2018

Introduction – Formic acid (FA) very abundant organic compound & the simplest carboxylic acid

Introduction – Formic acid (FA) very abundant organic compound & the simplest carboxylic acid • Widely used in chemistry • Abundant in the atmosphere and the ISM • Model system for the properties of carboxylic acids – Dimeric form dominant in the gas phase in standard conditions (STP): ~ 92%. • Peculiar thermodynamical properties. • Cyclic dimer (FAD) is an elementary system for the Concerted Proton transfer process. • IR bands of the dimer are unresolved at room temperature: spectral congestion + Doppler broadening. 2 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

Spectroscopic issues Prolate asymmetric top (κ ~ -0. 7) belonging to the C 2

Spectroscopic issues Prolate asymmetric top (κ ~ -0. 7) belonging to the C 2 h point group. No pure rotation spectrum; 12 IR and 12 Raman active modes. Concerted proton transfer with TS in D 2 h (~ G 8) Series hard to follow: Statistical weights (Ka, Kc) ee: eo: oe: oo = 1: 3: 9: 3 Rovibrational levels split into 2 tunneling states: lower (l) and upper (u) Selection rules different according to band type. Birer & Havenith, Annu. Rev. Phys. Chem. 2009, 60: 263– 75 3 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

Spectroscopic issues in the FIR range Low frequency intermolecular modes Rapid high density of

Spectroscopic issues in the FIR range Low frequency intermolecular modes Rapid high density of states. 4 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

Spectroscopic issues in the FIR range Jet-cooled conditions mandatory to rotationally resolve IR bands

Spectroscopic issues in the FIR range Jet-cooled conditions mandatory to rotationally resolve IR bands 5 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

Synchrotron-based jet-cooled far-IR spectrum of FAD • FTIR spectra: Bruker IFS 125 HR from

Synchrotron-based jet-cooled far-IR spectrum of FAD • FTIR spectra: Bruker IFS 125 HR from the AILES beamline at synchrotron SOLEIL Jet-AILES setup • Jet-AILES supersonic expansion • Experimental conditions v He carrier gas: 5 slm v Formic acid: 200 g / h v Stagnation pressure: 90 Torr v Température: 313 K v Trot ~ 30 K 6 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

Synchrotron-based jet-cooled far-IR spectrum of FAD jet, res. 0. 001 cm-1 jet, res. 0.

Synchrotron-based jet-cooled far-IR spectrum of FAD jet, res. 0. 001 cm-1 jet, res. 0. 005 cm-1 cell, res. 0. 1 cm-1 7 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

ISMS 2017 (M. Goubet): Intermolecular in-plane bending 340 co-added interferograms (~12 h of scans)

ISMS 2017 (M. Goubet): Intermolecular in-plane bending 340 co-added interferograms (~12 h of scans) recorded at max. resolution (10 -3 cm-1) using synchrotron radiation + 6 µm mylar beamsplitter + He-cooled Si bolometer. - exp. - sim. l l - sim. u u zoom in the Q branch zoom in the P branch. Qualitative agreement but fit far from experimental accuracy. 8 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

ISMS 2017 (C. Duan): A new Hamiltonian model for FAD ü Watson A-reduced asymmetric-top

ISMS 2017 (C. Duan): A new Hamiltonian model for FAD ü Watson A-reduced asymmetric-top in the Ir reduction ü C-type Coriolis interaction between u/l or +/- sublevels: ü Global analysis (1842 lines) to extract GS molecular parameters. ü STD = 0. 000 74 cm-1 9 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

The n 24 fundamental band of the cyclic formic acid dimer n 24 -

The n 24 fundamental band of the cyclic formic acid dimer n 24 - 0 band (This work) Ground state (Duan, 2017) E(24)+ E(24)- 263. 923 955(43) 263. 948 584(44) n 0 0. 202 927 2(71) 0. 2026307(84) A 0. 076 042 1(63) 0. 0760624(65) B 0. 054 804 083(100) 0. 054 803 248(104) C 1. 695(36) 0. 369(59) 106 DK 1. 166 5(98) 0. 914 5(108) 106 DJK - 3. 595(68) - 3. 385(81) 108 DJ - 2. 624(34) - 2. 663(41) 108 d. J J < 29, Ka < 14 1800 lines, STD = 0. 000 74 cm-1 0. 010959(37) Fab - 0. 024629 DE J < 42, Ka < 6 800 lines, STD = 0. 000 69 cm-1 10 Cm-1 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

The n 24 fundamental band of the cyclic formic acid dimer 241/2, 23 –

The n 24 fundamental band of the cyclic formic acid dimer 241/2, 23 – 251/2, 24 250/1, 25 – 260/1, 26 232/3, 21 – 242/3, 22 P-Branch doublets Observed Calculated Global agreement on the observed structure Q-branch structure: higher Ka values 11 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

The n 24 fundamental band of the cyclic formic acid dimer Conclusion - Pioneering

The n 24 fundamental band of the cyclic formic acid dimer Conclusion - Pioneering work on the n 22 fundamental band at 1200 cm-1 : Identification of the Concerted Proton transfer process (M. Havenith) - Using QCL IR spectroscopy in a supersonic expansion : effective model to reproduce the structure with doublet (c-type interaction) (C. Duan) - The present work : first observation and analysis of a FIR band of the cyclic formic acid dimer, the n 24 fundamental band at 263 cm-1 - To be done: assignment of the higher Ka lines (Q-branches) of the n 24 fundamental band - Ground state: Need for a global analysis of all IR and FIR data, using laser and FTIR spectra. 12 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

The present work is supported by the Programme d’Investissement d’Avenir through the Labex Ca.

The present work is supported by the Programme d’Investissement d’Avenir through the Labex Ca. PPA (ANR-LABX-0005 -01), the Contrat de Plan Etat Région CLIMIBIO, the Région Hauts-de-France, and the FEDER 13 ISMS – Urbana-Champaign (USA), June 18 -22, 2018 20/06/2018 – Thérèse HUET

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