High-Resolution Fourier Transform Infrared Absorption Spectroscopy of the ν<sub>6</sub> Band of c-C<sub>3</sub>H<sub>2</sub> Pradeep R. Varadwaj Ryuji Fujimori Kentarou Kawaguchi 10.1021/jp204068w.s001 https://acs.figshare.com/articles/dataset/High_Resolution_Fourier_Transform_Infrared_Absorption_Spectroscopy_of_the_sub_6_sub_Band_of_c_C_sub_3_sub_H_sub_2_sub_/2626462 The gas-phase high-resolution absorption spectrum of the ν<sub>6</sub> band of cyclopropenylidene (c-C<sub>3</sub>H<sub>2</sub>) has been observed using a Fourier transform infrared spectrometer for the first time. The molecule has been produced by microwave discharge in an allene (3.3 Pa) and Ar (4.0 Pa) mixture inside a side arm glass tube. The observed spectrum shows a pattern of c-type ro-vibrational transitions in which the Q-branch lines strongly and distinctly stand out in the spectrum. A combined least-squares analysis of the observed 216 ro-vibrational transitions together with 28 millimeter-wave rotational transitions from the previous study has resulted in an accurate determination of the molecular constants in the ν<sub>6</sub> state. The band center is found to be at 776.11622(13) cm<sup>–1</sup> with one standard deviation in parentheses, which is 2.3% lower than the matrix isolation value. The intensity ratio <i>I</i><sub>3</sub>(ν<sub>3</sub>)/<i>I</i><sub>6</sub>(ν<sub>6</sub>) obtained from the observed ν<sub>3</sub> and ν<sub>6</sub> bands, 1.90(9), is somewhat lower than the ratio estimated from ab initio (2.4–2.6) and DFT (2.8) calculations. 2011-08-04 00:00:00 side arm glass tube absorption spectrum Absorption Spectroscopy 3H microwave discharge intensity ratio ν6 state transition ν6 bands DFT Pa ν6 Band Fourier band center matrix isolation value ν6 band