An unbiased spectral line survey toward a solar-type Class 0/I protostar, IRAS04368+2557, in L1527 has been carried out in the 3 mm band with the Nobeyama 45 m telescope. L1527 is known as a warm ...carbon-chain chemistry (WCCC) source, which harbors abundant unsaturated organic species such as C\(_n\)H (\(n = 3,\ 4,\ 5,\ldots\)) in a warm and dense region near the protostar. The observation covers the frequency range from 80 to 116 GHz. A supplementary observation has also been conducted in the 70 GHz band to observe fundamental transitions of deuterated species. In total, 69 molecular species are identified, among which 27 species are carbon-chain species and their isomers, including their minor isotopologues. This spectral line survey provides us with a good template of the chemical composition of the WCCC source.
The rotational spectral lines of c-C$_3$H$_2$ and two kinds of the $^{13}$C
isotopic species, c-$^{13}$CCCH$_2$ ($C_{2v}$ symmetry) and c-CC$^{13}$CH$_2$
($C_s$ symmetry) have been observed in the ...1-3 mm band toward the low-mass
star-forming region L1527. We have detected 7, 3, and 6 lines of c-C$_3$H$_2$,
c-$^{13}$CCCH$_2$ , and c-CC$^{13}$CH$_2$, respectively, with the Nobeyama 45 m
telescope, and 34, 6, and 13 lines, respectively, with the IRAM 30 m telescope,
where 7, 2, and 2 transitions, respectively, are observed with the both
telescopes. With these data, we have evaluated the column densities of the
normal and $^{13}$C isotopic species. The c-C$_3$H$_2$/c-$^{13}$CCCH$_2$
ratio is determined to be $310\pm80$, while the
c-C$_3$H$_2$/c-CC$^{13}$CH$_2$ ratio is determined to be $61\pm11$. The
c-C$_3$H$_2$/c-$^{13}$CCCH$_2$ and c-C$_3$H$_2$/c-CC$^{13}$CH$_2$
ratios expected from the elemental $^{12}$C/$^{13}$C ratio are 60-70 and 30-35,
respectively, where the latter takes into account the statistical factor of 2
for the two equivalent carbon atoms in c-C$_3$H$_2$. Hence, this observation
further confirms the dilution of the $^{13}$C species in carbon-chain molecules
and their related molecules, which are thought to originate from the dilution
of $^{13}$C$^+$ in the gas-phase C$^+$ due to the isotope exchange reaction:
$\mathrm{^{13}C^++CO\rightarrow{}^{13}CO+C^+}$. Moreover, the abundances of the
two $^{13}$C isotopic species are different from each other. The ratio of
c-$\mathrm{^{13}CCCH_2}$ species relative to c-$\mathrm{CC^{13}CH_2}$ is
determined to be $0.20\pm0.05$. If $^{13}$C were randomly substituted for the
three carbon atoms, the c-$\mathrm{^{13}CCCH_2}$/c-$\mathrm{CC^{13}CH_2}$
ratio would be 0.5. Hence, the observed ratio indicates that
c-$\mathrm{CC^{13}CH_2}$ exists more favorably. Possible origins of the
different abundances are discussed.
The rotational spectral lines of c-C\(_3\)H\(_2\) and two kinds of the \(^{13}\)C isotopic species, c-\(^{13}\)CCCH\(_2\) (\(C_{2v}\) symmetry) and c-CC\(^{13}\)CH\(_2\) (\(C_s\) symmetry) have been ...observed in the 1-3 mm band toward the low-mass star-forming region L1527. We have detected 7, 3, and 6 lines of c-C\(_3\)H\(_2\), c-\(^{13}\)CCCH\(_2\) , and c-CC\(^{13}\)CH\(_2\), respectively, with the Nobeyama 45 m telescope, and 34, 6, and 13 lines, respectively, with the IRAM 30 m telescope, where 7, 2, and 2 transitions, respectively, are observed with the both telescopes. With these data, we have evaluated the column densities of the normal and \(^{13}\)C isotopic species. The c-C\(_3\)H\(_2\)/c-\(^{13}\)CCCH\(_2\) ratio is determined to be \(310\pm80\), while the c-C\(_3\)H\(_2\)/c-CC\(^{13}\)CH\(_2\) ratio is determined to be \(61\pm11\). The c-C\(_3\)H\(_2\)/c-\(^{13}\)CCCH\(_2\) and c-C\(_3\)H\(_2\)/c-CC\(^{13}\)CH\(_2\) ratios expected from the elemental \(^{12}\)C/\(^{13}\)C ratio are 60-70 and 30-35, respectively, where the latter takes into account the statistical factor of 2 for the two equivalent carbon atoms in c-C\(_3\)H\(_2\). Hence, this observation further confirms the dilution of the \(^{13}\)C species in carbon-chain molecules and their related molecules, which are thought to originate from the dilution of \(^{13}\)C\(^+\) in the gas-phase C\(^+\) due to the isotope exchange reaction: \(\mathrm{^{13}C^++CO\rightarrow{}^{13}CO+C^+}\). Moreover, the abundances of the two \(^{13}\)C isotopic species are different from each other. The ratio of c-\(\mathrm{^{13}CCCH_2}\) species relative to c-\(\mathrm{CC^{13}CH_2}\) is determined to be \(0.20\pm0.05\). If \(^{13}\)C were randomly substituted for the three carbon atoms, the c-\(\mathrm{^{13}CCCH_2}\)/c-\(\mathrm{CC^{13}CH_2}\) ratio would be 0.5. Hence, the observed ratio indicates that c-\(\mathrm{CC^{13}CH_2}\) exists more favorably. Possible origins of the different abundances are discussed.
