HIGH RESOLUTION OVERTONE SPECTROSCOPY OF THE ACETYLENE VAN DER WAALS DIMER, 12 (C 2 H 2 ) 2 K. D IDRICHE, C. L AUZIN, T. F ÖLDES, D. G OLEBOWSKI AND M. H ERMAN International Symposium on Molecular Spectroscopy 66th Meeting June 20-24, 2011 – Ohio State University C. L EFORESTIER Laboratoire de Chimie Quantique et Photophysique Université Libre de Bruxelles Belgium Institut Charles Gerhardt, Monpellier, France

FANTASIO+ C ONTINUOUS SUPERSONIC JET FTIR SPECTROMETER MASS SPECTROMETER CW CRDS SET - UP (1.5 µm) Fourier trANsform, Tunable diode and quadrupole mAss spectrometers interfaced to a Supersonic expansIOn Didriche et al., Mol. Phys., 2010, 108, 2155    C 2 H 2 :2CH

b a  (10 -6 cm -1 ) wavenumber (cm -1 ) rQ3(J)rQ3(J) rQ2(J)rQ2(J) rQ1(J)rQ1(J) rQ0(J)rQ0(J) pQ1(J)pQ1(J) pQ2(J)pQ2(J) pQ3(J)pQ3(J) pQ4(J)pQ4(J) unit 1 unit 2 b-type simulation (20K) PGOPHER (C. Western, University Of Bristol) Ground State*B state origin (cm-1) A (MHz) B (MHz) C (MHz)  JK (MHZ) *Fraser et al., J. Chem. Phys., 1988, 89, C 2 H 2 (6%)/Ar P 0 = 1.2 atm /slit Didriche et al., Mol. Phys., 2010, 108, 2155 Last year

b a  (10 -6 cm -1 ) wavenumber (cm -1 ) rQ3(J)rQ3(J) rQ2(J)rQ2(J) rQ1(J)rQ1(J) rQ0(J)rQ0(J) pQ1(J)pQ1(J) pQ2(J)pQ2(J) pQ3(J)pQ3(J) pQ4(J)pQ4(J) unit 1 unit 2 b-type simulation (20K) PGOPHER (C. Western, University Of Bristol) Ground State*B state origin (cm-1) A (MHz) B (MHz) C (MHz)  JK (MHZ) *Fraser et al., J. Chem. Phys., 1988, 89, C 2 H 2 (6%)/Ar P 0 = 1.2 atm /slit Didriche et al., Mol. Phys., 2010, 108, 2155 further investigation is needed... Last year

 = 0°  = 90°  = 180°  = 270° G.T. Fraser et al., J. Chem. Phys. 89 (1988) equivalent structures Not a rigid rotor !

G 16   tun = A B 1 + +E + Energy  T UNNELING SPLITTINGS

Spectrum Energy 9 1,9 10 1, , ,12 Energy 8 0,8 9 0,9 10 0, ,11 P(J) lines  ev  tun  rot  ns S TATISTICAL WEIGHTS

Spectral analysis

2 - 3 K’ a –K ’’ a S PECTRAL ANALYSIS

0 - 1 Spectrum Energy S PECTRAL ANALYSIS

wavenumber T rot = 23 k S PECTRAL ANALYSIS

T rot = 23 k S PECTRAL ANALYSIS No contribution from E +

T rot = 23 k S PECTRAL ANALYSIS 4 - 3

Energy 2CH 1CH GS 2200 (MHz) Energy  R ESULTS simulationrotational constants for each statetunneling splittings internal rotation is hindered by vibrational excitation

b a  (10 -6 cm -1 ) wavenumber (cm -1 ) rQ3(J)rQ3(J) rQ2(J)rQ2(J) rQ1(J)rQ1(J) rQ0(J)rQ0(J) pQ1(J)pQ1(J) pQ2(J)pQ2(J) pQ3(J)pQ3(J) pQ4(J)pQ4(J) unit 1 unit 2 b-type simulation (20K) PGOPHER (C. Western, University Of Bristol) Ground State*B state origin (cm-1) A (MHz) B (MHz) C (MHz)  JK (MHZ) *Fraser et al., J. Chem. Phys., 1988, 89, C 2 H 2 (6%)/Ar P 0 = 1.2 atm /slit F UTUR WORK

b a unit 1 unit 2 Ground State*A state origin (cm-1) A (MHz) B (MHz) C (MHz)  JK (MHZ) Fraser et al., J. Chem. Phys., 1988, 89, 6028 wavenumber (cm -1 ) a-type simulation PGOPHER (C. Western, University Of Bristol) a-type simulation + b-type simulation 2 CH stretches F UTUR WORK

A CKNOWLEDGEMENTS X. de Ghellinck Athéna Rizopoulos Patrick Van Poucke Baris Kizil Darius Golebiowski Fundings: -FNRS -ULB -Action de Recherches Concertées de la Communauté française de Belgique

J even, I H = 0 A1±A1± I H = 0 ; g I = 1 J even, I H = 0J odd, I H = 1 E±E± I H = 1 ; g I = 3 J odd, I H = 1J even, I H = 0 A2±A2± I H = 1 ; g I = 3 J odd, I H = 1 B2±B2± I H = 0,2 ; g I = 6 12 C 2 H C 2 H 2  evrt NS G.T. Fraser et al., J. Chem. Phys. 89 (1988) Results