Small carbon chain molecules like linear C₃ are thought to play a crucial role in the formation of larger, complex molecules, including pre-biotic species. The formation pathways of organic molecules with carbon chains as backbones is by far not well understood. Studies of isotope fractionation have proven to be a useful tool of tracing chemical reaction pathways and to elucidate formation and destruction processes of interstellar molecules. Recent velocity-resolved observations in the far-infrared have resulted in the detection of C₃ ro-vibrational transitions in the warm envelopes of star-forming hot cores W31C, W49N and DR21(OH). Multiple far-infrared transitions of C₃ have also been detected towards the Galactic center molecular clouds SgrB2(M) and Sgr B2(N). Since C⁺ is involved in an important step of the formation route of the C₃ molecule, it is likely that effects of isotopic fractionation of C⁺ will manifest itself in the ¹²C₃/¹³CCC and ¹²C₃/C¹³CC ratios as well. Based on high resolution THz- laboratory measurements of C₃ and its ¹³C-isotopologues conducted at the Kassel laboratories, we used the GREAT-receiver onboard SOFIA for a first ever detection of ¹³CCC towards SgrB2(M). In this talk we present results and possible implications of the observation.

Despite importance of the origin of life, long lasting challenges to detect the simplest amino acid glycine (H₂NCH₂COOH) in interstellar medium has not been successful. As a preliminary step toward search for glycine, detection of its precursor has received attention. It is considered that glycine is produced by the reaction of the HOCO radical and the aminomethyl radical(CH₂NH₂) on interstellar grain surface:
HOCO + CH₂NH₂ → H₂NCH₂COOH.     (1)

HOCO is produced by the reaction of OH + CO → HOCO and/or HCOOH → HOCO + H. However, HOCO and CH₂NH₂ have not been investigated in interstellar medium. Recently, we determined the accurate molecular constants of HOCO.T. Oyama et al., J. Chem. Phys. 134, 174303 (2011).hus, accurate rest frequencies were derived from the constants. In the present study, we carried out the observations of HOCO in the massive star-forming region Sgr B2(M), having variety of interstellar molecules, with Nobeyama 45 m radio telescope. Although HOCO could not be detected in Sgr B2(M), the upper limit of the column density was derived to be 9.0×10¹² cm⁻² via the spectrum in the 88 GHz region by the rotational diagram method. If the reaction (1) is a main process of the glycine production in this region, an extremely deep search is needed to detect glycine.

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Footnotes:

T. Oyama et al., J. Chem. Phys. 134, 174303 (2011).T

Isotopic ratio is a critical parameter in understanding galactic chemical evolution. In addition, carbon isotopic ratio of an organic molecule reflects its formation mechanism. In the present study, we observed the simplest cyanopolyyne HC₃N and its isotopomers in the massive star-forming region Sgr B2(M) with Nobeyama 45 m radio telescope. The column density and the rotational temperature of HC₃N were determined to be 1.6×10¹⁵ cm⁻² and 163 K, respectively. The ratios of the column densities for the ¹³C isotopomers were derived to be [H¹³CCCN]:[HC¹³CCN]:[HCC¹³CN] = 1:1.03(4):0.99(3), where the rotational temperature was fixed to that of HC₃N. The ratios are almost the same, suggesting no isotopic fractionation for the specific carbon atoms in HC₃N. Therefore, it is considered that the ¹³C isotope exchange reactions do not contribute to make difference among the column densities of the three ¹³C isotopomers in the relatively warm region of Sgr B2(M). In contrast, the reported ratios in TMC-1 and L1527 are 1:1.0(1):1.4(2)S. Takano et al., Astron. Astrophys. 329, 1156 (1998).nd 1:1.01(2):1.35(3),M. Araki et al., ApJ 833, 291 (2016).espectively, where the ratios show higher abundance of HCC¹³CN. We also observed the transitions in the vibrational excited states of HC₃N. The rotational temperature of 362 K in the ν₄, ν₅, ν₆ and ν₇ excited states was obviously different from that of the vibrational ground state.

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Footnotes:

S. Takano et al., Astron. Astrophys. 329, 1156 (1998).a M. Araki et al., ApJ 833, 291 (2016).r

Observations from a spectral-line survey of Sgr B2(N) of the ¹²C and ¹³C isotopologues of H₂CS, CH₃CCH, NH₂CHO, CH₂CHCN, and CH₃CH₂CN have been analyzed to more accurately establish the ¹²C/¹³C ratio in this cloud. The wide spectral coverage has enabled an accurate evaluation of the ¹²C/¹³C ratios in these low abundance molecules, based on numerous transitions. The lines typically exhibited two distinct velocity components at 64 and 73 km s⁻¹. The ¹²C/¹³C ratio was found to be in the range 18-24 for all 5 molecules, for optically thin transitions, with an average value of 20.5, and did not significantly vary between the two velocity components. The Galactic gradient has been revised to be ¹²C/¹³C = 6.08(0.48) D_GC + 15.7(2.9). Furthermore, the ¹²C/¹³C ratio did not change with substitution site on the molecule. Therefore, there appears to be very little chemical fractionation or isotope-selective photodissociation occurring in Sgr B2(N), and the ¹²C/¹³C ratios are a true reflection of the isotopic abundances generated by stellar nucleosynthesis.

Deuterium fractionation increases significantly in cold (T < 25 K), dense (n_H > 10⁴  cm⁻³) molecular clouds, in which molecules like CO freeze out onto dust grains leading to an enhanced abundance of H₂D⁺, D₂H⁺ and D₃⁺. c-C₃H₂ is formed and deuterated exclusively by gas-phase chemistry. This makes it to a very good indicator of gas-phase deuteration and therefore to an excellent tool to study the early phases of star formation. We observed the c-C₃HD/c-C₃H₂ ratio toward 13 prestellar and 4 protostellar cores in the Taurus and Perseus Complex, respectively. In particular, the 3_0,3−2_1,2 and 2_1,2−1_0,1 transitions of the isotopologues c-C₃HD and c-¹³CC₂H₂ were observed in all prestellar and protostellar cores with a very high S/N. In both samples a high deuteration factor was found. In the prestellar cores the c-C₃HD/c-C₃H₂ ratio varies between 5% and 13% while in protostellar cores is found to be 9%-23%. I will present our results on the correlation between the deuterium fractionation of c-C₃H₂ and evolutionary indicators such as central density and dust temperature and compare them with the deuteration of N₂H⁺ observed in the same sources.

Carbon chains in the warm carbon chain chemistry (WCCC) region has been searched in the 42-44 GHz region by using Green Bank 100 m telescope. Long carbon chains C₇H, C₆H, CH₃CCCCH, and linear-C₆H₂ and cyclic species C₃H and C₃H₂O have been detected in the low-mass star forming region L1527, performing the WCCC. C₇H was detected for the first time in molecular clouds. The column density of C₇H is derived to be 6.2 ×10¹⁰ cm⁻² by using the detected J = 24.5-23.5 and 25.5-24.5 rotational lines. The ²Π_1/2 electronic state of C₆H, locating 21.6 K above the ²Π_3/2 electronic ground state, and the K_a = 0 line of the para species of linear-C₆H₂ were also detected firstly in molecular clouds. The column densities of the ²Π_1/2 and ²Π_3/2 states of C₆H in L1527 were derived to be 1.6 ×10¹¹ and 1.1 ×10¹² cm⁻², respectively. The total column density of linear-C₆H₂ is obtained to be 1.86 ×10¹¹ cm⁻². While the abundance ratios of carbon chains in between L1527 and the starless dark cloud Taurus Molecular Cloud-1 Cyanopolyyne Peak (TMC-1 CP) have a trend of decrease by extension of carbon-chain length, column densities of CH₃CCCCH and C₆H are on the trend. However, the column densities of linear-C₆H₂, and C₇H are as abundant as those of TMC-1 CP in spite of long carbon chain, i.e., they are not on the trend. The abundances of linear-C₆H₂ and C₇H show that L1527 is rich for long carbon chains as well as TMC-1 CP.

The Diffuse Interstellar Bands (DIBs) are hundreds of spectral lines observed in sightlines towards many stars in the optical and near-infrared. Although most of these transitions remain unassigned, four of them have recently been assigned to C₆₀⁺ and C₇₀⁺. In earlier observations of the visible spectrum of the extragalactic supernova SN 2012ap, we observed changes in the equivalent widths of DIBs on the timescale of its light curve, which indicated that some DIB carriers might exist closer to massive stars then previously believed. Motivated by these findings, we undertook a pathfinder survey of 17 massive stars with the Tillinghast Reflector Echelle Spectrograph at Fred L. Whipple Observatory in search of temporal variability in DIBs. In 3 of the 17 stars, we found possible evidence for variation in line substructure of DIBs λ5797 and λ6614. In this talk, we will discuss our efforts to model λ5797 toward MT-59 using contour simulations based on previously published spectral models from higher resolution observations. Although the SNR of this spectrum was only 5-15, our preliminary results suggest that the variations in molecular spectra over time might arise from changes in carrier temperature. These early results demonstrate the need for higher SNR spectra taken at multiple epochs to further explore potential temporal variability. If successful, time-variation could provide additional evidence to assist in identifying DIB carriers.

In deriving the simple formula, ζL=2k_eN(H₃⁺)(n_C/n_H)_SVR/f(H₂), used to estimate cosmic ray H₂ ionization rate ζ from observed H₃⁺ column density N(H₃⁺) in the Central Molecular Zone (CMZ) of the Galactic center (GC),Oka, T., Geballe, T. R., Goto, M., Usuda, T., McCall, B. J. 2005, ApJ, 632, 882he following two effects were neglected: (1) the charge exchange reaction H₂⁺ + H → H₂ + H⁺Indriolo, N., McCall, B. J. 2012, ApJ, 745:91hich significantly reduces H₃⁺ production rate if the fraction of molecular hydrogen f(H₂) is much lower than 1, and (2) the production of electrons from ionization of H₂ and H which greatly increases the H₃⁺ destruction rate if ζ is much higher than 10⁻¹⁵ s⁻¹. (Only electrons from VUV first ionization of C atoms had been considered). Recent more extensive analysis using the Meudon PDR code by Le Petit et al.Le Petit, F., Ruaud, M., Bron, E., Godard, B., Roueff, E., Languignon, D., Le Bourlot, J. 2016, A&A, 585, A105as indicated that these effects are not negligible in the CMZ. While an extensive chemical model calculation is beyond the scope of our analysis, we have attempted to use our simple model considering only hydrogenic species and electrons to take these two effects into account. When (1) is introduced, the rate of H₃⁺ production is approximated to be ζn_H[f(H₂)]²,Oka, T. 2013, Chem. Rev. 113, 8738hich is  ∼  3 times lower than the previous value for f(H₂) = 0.6 reported by Le Petit et al.^c When (2) is taken into account, the electron number density is approximated to be n_e = n_CR + ζn_H/[2k_en(H₃⁺)] where the first and second term represents electrons from the C atoms and those from H₂ and H, respectively. The first term (in which R represents the increase of metallicity from the solar vicinity to the GC, R ≥ 3) has the electron fraction x_e = 5 × 10⁻⁴ and the second term becomes significant at ζ  ∼  10⁻¹⁵ s⁻¹. This introduces a non-linearity between ζ and N(H₃⁺) and the latter reaches a maximum at ζ  ∼  10⁻¹⁴ s⁻¹ and decreases as ζ increases further. Application of the results to the observed N(H₃⁺) will be discussed.

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Footnotes:

Oka, T., Geballe, T. R., Goto, M., Usuda, T., McCall, B. J. 2005, ApJ, 632, 882t Indriolo, N., McCall, B. J. 2012, ApJ, 745:91w Le Petit, F., Ruaud, M., Bron, E., Godard, B., Roueff, E., Languignon, D., Le Bourlot, J. 2016, A&A, 585, A105h Oka, T. 2013, Chem. Rev. 113, 8738w

The elusive protonated oxygen, O₂H⁺, has been characterized by vibrational action spectroscopy in a cryogenic 22-pole ion trap. On the one hand, the vibrational bands of the tagged He-O₂H⁺ have been investigated, using a table-top OPO system for the known OH-stretch^a, whereas the FELIX^b light source has been used to detect the hitherto unknown low-frequency O-O-H bend and O-O stretch. On the other hand, the untagged O₂H⁺ has been detected for the first time by high-resolution rovibrational spectroscopy via its ν₁ OH-stretch motion. 38 ro-vibrational fine structure transitions with partly resolved hyperfine satellites were measured (56 resolved lines in total). Spectroscopic parameters were determined by a fit to an asymmetric rotor model with a ³A" electronic ground state. The band center is at 3016.73 cm⁻¹, which is in good agreement with experimental^a and ab initio^c,d predictions. Based on the spectroscopic parameters, the rotational spectrum is predicted, but not detected yet.
^a S. A. Nizkorodov et al., Chem. Phys. Lett., 278, 26, 1997
^b D. Oepts et al., Infrared Phys. Technol., 36, 297, 1995
^c S. L. W. Weaver et al., Astrophys. J., 697, 601, 2009
^d X. Huang and T. J. Lee, J. Chem. Phys., 129, 044312, 2008