Fourier Transform Infrared Spectral Investigation of the 6 Band of cyclic-C3H2 Pradeep R Varadwaj, Ryuji Fujimori, Kentarou Kawaguchi Molecular Spectroscopy Laboratory, Department of Chemistry, Faculty of Sciences Okayama University, Japan FB11, page-290 65th Meeting – June 21-25, 2010 International Symposium on Molecular Spectroscopy
A species of interstellar interest c-C3H2 molecule: A species of interstellar interest Interesting because that it is highly reactive importance in organic chemistry Its occurrence in the interstellar medium ( diffuse clouds, Cold quiescent clouds, star forming regions etc.) The major formation reaction of c-C3H2 is the dissociative recombination of c-C3H3+ C3H3+ + e- → C3H2 + H c-C3H3+ is a product of a long chain of carbon chemistry that occurs in the ISM.
Studies so far First experimental matrix isolation infrared detection was done by Reisenauer et al. in 1984 Bands at 1279, 1063, 888, and 789 cm-1 were confirmed. Astronomical detection (P. Thaddeus et al Astrophys. J. Lett. 299, L63 (1985)) Microwave study: Bogey et. al CPL 126 (1985); 118-411 GHz region (studies of 13C and D isotopomers leads to molecular structure) Stark measurement: Saito et al CPL 140 (1987): determination of (3.43D) Millimeter-wave study: 85-400 GHz region (ground and several excited states, R. Mollaaghababa et al, JCP 99 （1993)) 6. High-resolution study: Hirahara et al JCP 95 (1991) ; 1000-1330 cm-1 region; confirming the band at 1277.3711(1) cm-1 Ab initio /DFT results suggest that the band at 789 cm-1 should be observable. The band Intensity is about 2.4 times less intense than that observed at 1277 cm-1. Motivation: An accurate determination of the centrifugal distortion constants To assign the band and that to determine the origin of this band.
Molecular Constants of c-C3H2 in the ground and four vibrationally excited states R. Mollaaghababa, C. A. Gottlieb, J. M. Vrtilek, P Thaddeus J. Chem. Phys. 99 (1993) 890
The calculated FTIR spectrum of the 6 band of c-C3H2 B1 symmetry In phase out-of-pane CH vibrations R-branch P-branch Q-branch C-type spectrum
Experimental Arrangements Production of c-C3H2
An Observed FTIR Spectrum of c-C3H2 in the region 775.4-776.5 cm-1
The FTIR spectrum of c-C3H2
Calculated spectrum Subtracted spectrum A comparison
A part of the FTIR spectrum of c-C3H2 Q(1-14) Q(29) Q(16) Q(27) Q(21) Q(25) Q(23) Q(19) Q(5) Q(7) Q(6) Q(8) Q(13) Q(11) Q(9) Q(10) Ka,Kc = 0,1 Ka,Kc = 1,2 16 0 16 16 1 16 A part of the FTIR spectrum of c-C3H2
Few Q-branch lines strongly & distinctly stand out in the spectrum J Ka Kc J' Ka' Kc' Calc. Obs. Diff.
Ro-vibrational Parameters derived from a simultaneous fit This work Millimeter-wave dataa A B C J 103 JK 103 K 103 J 103 K 103 HJ 103 HJK 106 HKJ 106 HK 106 h1 106 h2 106 h3 106 0 (uÅ2) v6 (cm-1) N 34157.134(49) 31944.414(49) 16778.026(4) 209.66(44) -409.1(3) -511.4(40) 100.61(22) 40.06(8) 0.00 37.1(19) -150(11) 112(15) 0.499(33) -0.88c 1.22c -0.494951 776.11729(7) 357(332+25) 34157.232(61) 34944.546(75) 16777.999(10) 210.388(3) -412.809(5) -499.149(14) 101.037(1) 41.313(4) 6.37b -14.7b 10.08b 0.477b -0.88b 1.22b -0.494643(46) --- 28 a Mollaaghababa et al; J. Chem. Phys. 99 (1993) 890-896 b Fixed to the ground state values
Summary Cyclic-C3H2 has been produced through microwave discharge of Allene (25 mTorr) in Ar (30 mTorr) The FTIR high-resolution absorption spectrum has been observed and assigned. A simultaneous fitting of the assigned transitions of this work along with the rotational transitions from a previous study resulted in an accurate determination of the ro-vibrational constants. A good agreement is found between the results of this work and those reported by R. Mollaaghababa et al J. Chem. Phys. 99 (1993) 890 except higher order distortion constants. The band origin of the 6 band is found to be at 776.1 cm-1 Acknowledgement Thanks Japan Society for the promotion of Science (JSPS) for funding and scholarship
9 stable isomers of the Singlet and triplet c-C3H2 Mohajeri et al. J. Mol. Struct: Theochem 820 (2007) 65-73