Shin-Ichi Ishikawa

A survey of CCS, HC3N, HC5N, and NH3 toward dark cloud cores and their production chemistry

Survey observations of CCS (J N = 4 3 -3 2 , J N = 2 1 -1 0 ), HC 3 N (J = 5-4), HC 5 N (J = 9-8, J = 17-16), and NH 3 (J, K = 1, 1) were carried out toward 49 dark cloud cores to examine the existence of a systematic relation between the chemical evolution and the physical evolution of dark clouds. The J N = 3 3 -2 2 and J N = 3 4 -2 3 lines of CCS and the J = 4-3 line of C 3 S were also observed in several cores

Mapping observations of sulfur-containing carbon-chain molecules in Taurus Molecular Cloud 1 (TMC-1)

High-resolution mapping observations were carried out toward Taurus Molecular Cloud 1 (TMC-1) with sulfur-containing carbon-chain molecules, CCS and C 3 S, and other molecules, CS, C 34 S, HCS + , HC 3 N, HC 5 N, C 4 H, and NH 3 , to investigate detailed molecular distribution and physical structure of the cold dark cloud.

Laboratory and astronomical detection of the cyclic C3H radical

Laboratory and astronomical detections of the rotational spectrum of the cyclic C/sub 3/H radical are reported, and the formation process by ion-molecular reactions is discussed. Laboratory production of the radical involved the discharging of a mixture of C/sub 2/H/sub 2/, CO and He, following which 49 lines were assigned and the molecular constants determined. The astronomical search was conducted using the 2(12)-1(11) transition at 91.5 GHz whose four fine and hyperfine components have been detected toward TMC-1. A column density estimation of 6 x 10 to the 12th/sq cm has been obtained for the cyclic C/sub 3/H. 21 references.

Detection of isocyanoacetylene HCCNC in TMC-1

The linear HCCNC molecule, an isomer of cyanoacetylene HCCCN, has been detected in TMC-1 with the Nobeyama 45 m telescope using recent laboratory data reported in 1991 by Kruger et al. The column density of HCCNC in TMC-1 is determined to be 2.9(0.2) × 10 12 cm -2 which is 20-60 times smaller than that of HCCCN

Detection of a new carbon-chain molecule, CCO

We have detected a new carbon-chain molecule, CCO(3 sigma-), in the cold, dark molecular cloud TMC-1. The excitation temperature and the column density of CCO are, respectively, approximately 6 K and approximately 6 x 10(11) cm-2. This column density corresponds to a fractional abundance relative to H2 of approximately 6 x 10(-11). This value is two orders of magnitude less than the abundance of the related carbon-chain molecule CCS, and about half that of C3O. The formation mechanism for CCO is discussed.

Rotational spectrum of the CCS radical studied by laboratory microwave spectroscopy and radio-astronomical observations

The rotational spectral lines of the CCS radical and its isotopic species, CC(S-34), (C-13)CS, and C(C-13)S, have been observed in the laboratory, and the J(N) = 4(3)-3(2), J(N) = 2(1)-1(0), and J(N) = 3(4)-2(3) transitions for CCS and that of J(N) = 4(3)-3(2) for CC(S-34) have been observed toward a cold dark cloud, L1498. The molecular constants of CCS, CC(S-34), (C-13)CS, and C(C-13)S have been determined from the observed transition frequencies, and the rest frequencies of CCS and CC(S-34) below 300 GHz are listed with their line strengths. The frequencies of the low-N transitions of (C-13)CS and C(C-13)S are calculated for future astronomical observations. 19 refs.

Laboratory microwave spectroscopy of the linear C3H and C3D radicals and related astronomical observation

Laboratory observations of rotational spectral lines of the C{sub 3}H and C3D radicals in their ground and vibrationally excited states are compared with astronomical observations with the Nobeyama Radio Observatorys 45-m radio telescope carried out toward IRC + 10216 in May 1988. The C{sub 3}H radical is found to have an extremely low vibrationally excited state, nu4(2Sigma mu), caused by the Renner-Teller effect in the nu4 (CCH bending) state. The radio telescope observations failed to detect the lines of the vibrationally excited C3H at the rms noise level of 24 mK. The upper limit to the column density of the nu4(2Sigma mu) is estimated to be 3 x 10 to the 12th/sq cm. 27 refs.

Identification of the interstellar cyanomethyl radical (CH2CN) in the molecular clouds TMC-1 and Sagittarius B2

We report the astronomical identification of the cyanomethyl radical, CH2CN, the heaviest nonlinear molecular radical to be identified in interstellar clouds. The complex fine and hyperfine structures of the lowest rotational transitions at about 20.12 and 40.24 GHz are resolved in TMC-1, where the abundance appears to be about 5 x 10(-9) relative to that of H2. This is significantly greater than the observed abundance of CH3CN (methyl cyanide) in TMC-1. In Sgr B2 the hyperfine structure is blended in the higher frequency transitions at 40, 80, and 100 GHz, although the spin-rotation doubling is clearly evident. Preliminary searches in other sources indicate that the distribution of CH2CN is similar to that for such carbon chain species as HC3N or C4H.

Detection of HNCCC in TMC-1

The HNCCC molecule, an isomer of cyanoacetylene HCCCN, has been identified in TMC-1 through the observations with the Nobeyama 45 m telescope, considering the observed spectral pattern, results of ab initio calculations, and laboratory microwave spectroscopy. The column density of HNCCC in TMC-1 has been determined to be 3.8(0.6)×10 11 cm −2 , which is 160-450 times smaller than that of HCCCN

Detection of intense unidentified lines in TMC-1

A wide-band microwave spectral scan of TMC-1 has been performed for the first time using the Nobeyama 45 m telescope and two 16,000 channel acoustooptical radio spectrometers for the frequency regions of 22-24 GHz and 36-50 GHz. Seven strong lines which could not be identified with any known molecules, including the U45379 reported by Suzuki et al. (1984), were detected. The profiles of the unidentified lines are shown and their observed parameters are summarized. 10 references.