Pure rotational spectra of trans- and cis-HOCO have been observed by Fourier transform microwave spectroscopy and the millimeter-wave double resonance technique, where gas phase spectra of the cis-conformer were observed for the first time. These radicals were produced in a supersonic jet by discharging a mixture gas of CO and H(2)O diluted in Ar. The molecular constants including the fine and hyperfine constants have been precisely determined for both conformers. Deuterated analogs have also been observed. The determined r(0) structures agree with these of ab initio calculations. The Fermi contact constants show a difference of the unpaired electron densities on the protons between the two conformers. Intensity of the spectrum for cis-HOCO was compared with that of trans-HOCO, leading to a conclusion that both conformers were produced nearly equally in abundance under the present experimental conditions.

Using the Green Bank 100 m telescope and the Nobeyama 45 m telescope, we have observed the rotational emission lines of the three 13 C isotopic species of HC3N in the 3 and 7 mm bands toward the low-mass star-forming region L1527 in order to explore their anomalous 12 C/ 13 C ratios.The column densities of the 13 C isotopic species are derived from the intensities of the J = 5-4 lines observed at high signal-to-noise ratios. The abundance ratios are determined to be 1.00:1.01 ± 0.02:1.35 ± 0.03:86.4 ± 1.6 for [H 13 CCCN]:[HC 13 CCN]:[HCC 13 CN]: [HCCCN], where the errors represent one standard deviation. The ratios are very similar to those reported for the starless cloud, Taurus Molecular Cloud-1 Cyanopolyyne Peak (TMC-1 CP). These ratios cannot be explained by thermal equilibrium, but likely reflect the production pathways of this molecule.We have shown the equality of the abundances of H 13 CCCN and HC 13 CCN at a high-confidence level, which supports the production pathways of HC3N via C2H2 and C2H2 + . The average 12 C/ 13 C ratio for HC3N is 77 ± 4, which may be only slightly higher than the elemental 12 C/ 13 C ratio.Dilution of the 13 C isotope in HC3N is not as significant as that in CCH or c-C3H2. We have also simultaneously observed the DCCCN and HCCC 15 N lines and derived the isotope ratios:[DCCCN]/[HCCCN] = 0.0370 ± 0.0007 and [HCCCN]/[HCCC 15 N] = 338 ± 12.

Long carbon-chain molecules were searched for toward the low-mass star-forming region L1527, which is a prototypical source of warm carbon-chain chemistry (WCCC), using the 100 m Green Bank Telescope. Long carbon-chain molecules, C7H (2Π1/2), C6H (2Π3/2 and 2Π1/2), CH3C4H, and C6H2 (cumulene carbene, CCCCCCH2), and cyclic species of C3H and C3H2O were detected. In particular, C7H was detected for the first time in molecular clouds. The column density of C7H is determined to be 6 × 1010 cm−2. The column densities of the carbon-chain molecules including CH3C4H and C6H in L1527 relative to those in the starless dark cloud Taurus Molecular Cloud-1 Cyanopolyyne Peak (TMC-1 CP) tend to be systematically lower for long carbon-chain lengths. However, the column densities of C7H and C6H2 do not follow this trend and are found to be relatively abundant in L1527. This result implies that these long carbon-chain molecules are remnants of the cold starless phase. The results—that both the remnants and WCCC products are observed toward L1527—are consistent with the suggestion that the protostar can also be born in the parent core at a relatively early stage in the chemical evolution.

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Methanol (CH3OH) is an abundant interstellar species and is known to be an important precursor of various interstellar complex organic molecules. Among the methanol isotopologues, CH2DOH is one of the most abundant isotopologues and it is often used to study the deuterium fractionation of CH3OH in interstellar medium. However, the emission lines of CH2DOH can sometimes be optically thick, making the derivation of its abundance unreliable. Therefore, observations of its presumably optically thin 13C substituted species, 13CH2DOH, are essential to overcome this issue. In this study, the rotational transitions of 13CH2DOH have been measured in the millimeter-wave region from 216 GHz to 264 GHz with an emission-type millimeter- and submillimeter-wave spectrometer by using a deuterium and 13C enriched sample. The frequency accuracy of measured 13CH2DOH is less than a few kHz, and the relative line intensity error is less than 10% in most of the frequency range by taking advantage of the wide simultaneous frequency-coverage of the emission-type spectrometer. These results offer a good opportunity to detect 13CH2DOH in space, which will allow us to study the deuterium fractionation of CH3OH in various sources through accurate determination of the CH2DOH abundance.