A. Van Orden

Infrared laser spectroscopy of jet-cooled carbon clusters: structure of triplet C6

We report the first structural characterization of the triplet isomer of C6. Forty-one rovibrational/fine structure transitions in the nu 4(sigma u) antisymmetric stretch fundamental of the C6 cluster have been measured by diode laser absorption spectroscopy of a supersonic carbon cluster beam. The observed spectrum is characteristic of a centrosymmetric linear triplet state with cumulene-type bonding. The measured ground state rotational constant B0 = 0.048 479 (10)cm-1 and the effective bond length r(eff) = 1.2868 (1) angstroms are in good agreement with ab initio predictions for the linear triplet (3 sigma g-) state of C6.

Interstellar Detection of CCC and High-Precision Laboratory Measurements near 2 THz

We describe more fully our original tentative interstellar detection of the triatomic pure carbon chain molecule, CCC, in absorption toward the Galactic center source Sgr B2. C3 was detected with the Kuiper Airborne Observatory (KAO) by observing the R(2) bending vibration-rotation transition (0, 1 1 ,0 0, 0 0 , 0) near 65.7 cm 1 during one ) R ( of the last flights of KAO. The R(2) absorption line detected toward Sgr B2 is centered at 63.7(5) km s 1 , with km s 1 and a peak absorption of 18(3)%. This original tentative interstellar detection of C 3 DV(FWHM)p 8.3(9) has recently been confirmed by J. Cernicharo et al. through observation of a total of nine absorption lines, including the same R(2) line with the Infrared Space Observatory . We also present highly precise new laboratory measurements of 10 rovibrational transition frequencies of the n2 bending mode of C3, which have been obtained with the Cologne Sideband Spectrometer for Terahertz Application. Subject headings: ISM: individual (Sagittarius B2) — ISM: molecules — line: identification — methods: laboratory — techniques: spectroscopic On-line material: color figure

The ν5 band of C7

Abstract Twenty-four rotational lines a associated with the ν 5 (σ u ) antisymmetric stretch vibration of C 7 have been measured by high resolution diode laser absorption spectroscopy of a supersonic carbon cluster beam. A simultaneous fit of spectra connecting the ground state with ν = 1 of ν 4 (J.R. Heath , Science 249 (1990) 895, J.R. Heath and R.J. Saykally, J. Chem. Phys. 94 (1991) 1724 and ν 5 produces the following molecular constants for the ν 5 state (in cm −1 ): ν 5 =1898.3758(8), B′ =0.030556(15), D′ = -0.16(11) × 10 −7 , H′ = −0.44(31) × 10 −11 .

Infrared laser spectroscopy of jet‐cooled carbon clusters: The bending dynamics of linear C9

We report improved measurements for the nu 6 antisymmetric stretch fundamental and observation of the (nu 6 + nu 15)-nu 15 and (nu 6 + 2 nu 15)-2 nu 15 hot bands of the linear C9 carbon cluster by direct absorption diode laser spectroscopy of a supersonic carbon cluster beam. Analysis of these bands characterizes C9 as a semirigid molecule with a bending potential similar to that of C5 and further evidences the alternation in degree of rigidity of linear carbon clusters with the g-u symmetry of the HOMO.

Toward the detection of pure carbon clusters in the ISM

The questions of how and in what form that carbon is distributed in the Universe are critical ones for understanding the evolution of dust and planets, and for elucidating the origin of life on Earth and the prospects for discovering it elsewhere in the cosmos. While the abundant CI and CII atoms and CO molecule, which together account for a large fraction of the total carbon budget, have been thoroughly studied in many sources, and a large number of organic molecules have been detected in cold dust clouds, two potentially large reservoirs of carbon remain essentially unexplored. These are the PAH’s and pure carbon clusters. The former are strongly suspected to be important components of interstellar dust, while the latter have essentially been ignored. Most probably, this simply reflects the fact that relatively little information exists regarding the structures, properties, and in particular, on the transition freauencies of pure carbon clusters that would permit their study by astrophysical methods. The work described below’is designed to mitigate these deficiencies through the study of pure carbon clusters (C,) in the size range n=3-20 by high resolution infrared (350-3000 cm-‘) and far infrared (lo-350 cm-‘) laser spectroscopy. The specific goal of this work is to provide a precise inventory of laboratory frequencies and physical properties for these carbon clusters, such that a serious effort can be made to detect them in cold interstellar sources by far-IR astronomy.