D. Zhao, K.D. Doney, H. Linnartz Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, the Netherlands T he 3 μm Infrared Spectra of Propyne (C 3 H 4 ) Champaign-Urbana June 20, 2014 The 69th International Symposium on Molecular Spectroscopy FE09: ν 3 + ν 8 combination band FE10: ν 1 of 13 C-isotopologues

Propyne (methyl acetylene): H 3 C–C ≡ CH Identified in the interstellar medium and in the atmosphere of Titan An important constituent of fuels Intramolecular vibrational redistribution (IVR) dynamics Extensive studies on the rovibrational spectra of propyne in its electronic ground state have been performed in the microwave (MW), infrared (IR) and optical regions

Experimental setup Pulsed Plasma cw-OPO, linewidth 1 W cw cavity ring-down spectroscopy (cw-CRDS) (Zhao et al., CPL, 2013, 565, 132)

Overview spectra with discharge 0.5% C 3 H 4 /He, ~-600 V/ 300 mA v 1 (1 0 1 )

ν 3 + ν 8 combination band Estimated to be ~3175 cm -1 E–A 1 perpendicular transition 0.5% C 3 H 4 /He/Ar, without discharge

Rotational analysis (Zhao et al., CPL, 2014, 595, 256)

Reduced rotational level energies in ν 3 +ν 8 Near-resonant or non-resonant perturbations (z-axis Coriolis coupling type) (Zhao et al., CPL, 2014, 595, 256)

ν 1 fundamental band Fermi resonance ( ν 1 ~ ν 3 + 2ν 9 ) Non-resonant perturbations (z-axis Coriolis coupling type) for the main isotopologue 12 C 3 H 4 ( Kerstel et al., JCP, 1994, 100, 2588 ) High resolution data for ν 1 of 13 C-isotopologues are limited Only a few rovibrational transition lines of 13 CH 3 –C ≡ CH were mentioned in the experimental study on the C 3 H 4 -Ar complex by Blake et al. ( JCP, 1993, 98, 6031 ) (Duncan et al., 1976, 32, 255)

Experiment Cw-CRDS Gas mixture: C 3 H 4 diluted in He : Ar ~ (50: 50) [C 3 H 4 ]% ~ 0.02% - 0.5%, 13 C at natural abundance Continuous jet expansion using a 50 μm × 32 mm slit and ~0.5 bar backing pressure

Experimental spectrum I: ~ 0.02% C 3 H 4 Well consistent with previous jet-cooled spectrum of 12 C 3 H 4, except a small shift of cm -1 for the all rovibrational lines Additional measurement on H 2 O absorptions lines in this region, by adding 0.5% H 2 O vapor in the gas mixture, confirms the reliability of the absolute IR frequency calibration * * *

Experimental spectrum II: ~ 0.5% C 3 H 4 /He/Ar

Results: , hot band, C 3 H 4 -Ar complex 13 CH 3 –C ≡ CH: cm -1 ( ν 1 ), [~ cm -1 ( ν 3 + 2ν 9 0 )] CH 3 – 13 C ≡ CH: cm -1 ( ν 3 + 2ν 9 0 ), cm -1 ( ν 1 ) CH 3 –C ≡ 13 CH: cm -1 ( ν 1 ), cm -1 ( ν 3 + 2ν 9 0 )

CH 3 – 13 C≡CH ( ν 3 + 2ν 9 0 ) CH 3 –C≡ 13 CH ( ν 1 ) T rot ~ 9K Mainly K = 0 and 1 transitions are unambiguously assigned Relative band intensities allow to evaluate the Fermi resonance.

Discussion: Fermi resonance 13 CH 3 –C≡CH CH 3 – 13 C≡CH CH 3 –C≡ 13 CH

Discussion: Force field calculations predict the vibration-rotation constants 1 A = A 0 – A 1 at the order of cm -1 Experimentally determined values: 13 CH 3 –C≡CH: A 0 – A 1 = cm -1 CH 3 – 13 C≡CH: A 0 – A 1 ≈ 0 CH 3 –C≡ 13 CH: A 0 – A 1 = cm -1 z-axis Coriolis coupling type perturbations for 13 CH 3 –C≡CH and CH 3 –C≡ 13 CH.

Conclusions High resolution IR spectra of ν 3 + ν 8 of 12 C 3 H 4, and ν 1 of the three 13 C-isotopologues in supersonic slit-jet expansions Spectroscopic constants Fermi resonance and perturbations

ACKNOWLEDGEMENTS Financial support: NWO-VICI NOVA Dutch Astrochemistry Network. Thank you for your attention! Prof. dr. H. Linnartz K.D. Doney R. Auchettel ( Melbourne/Leiden)