Sakai et al. have observed long-chain unsaturated hydrocarbons and cyanopolyynes in the low-mass star-forming region L1527, and have attributed this result to a gas-phase ion-molecule chemistry, termed "Warm Carbon Chain Chemistry", which occurs during and after the evaporation of methane from warming grains. The source L1527 is an envelope surrounding a Class 0/I protostar with regions that possess a slightly elevated temperature of ≈ 30 K. The molecules detected by Sakai et al. are typically associated only with dark molecular clouds, and not with the more evolved hot corino phase. In order to determine if L1527 is chemically distinct from a dark cloud, we compute models including various degrees of heating. The results indicate that the composition of L1527 is somewhat more likely to be due to "Warm Carbon Chain Chemistry" than to be a remnant of a colder phase. If so, the molecular products provide a signature of a previously uncharacterized early phase of low mass star formation, which can be characterized as a "lukewarm" corino. We also include predictions for other molecular species that might be observed toward candidate lukewarm corino sources. Although our calculations show that unsaturated hydrocarbons and cyanopolyynes can be produced in the gas phase as the grains warm up to -2 -30 K, they also show that such species do not disappear rapidly from the gas as the temperature reaches 200 K, implying that such species might be detected in hot corinos and hot cores.

We investigate the water deuteration ratio and ortho-to-para nuclear spin ratio of H 2 (OPR(H 2 )) during the formation and early evolution of a molecular cloud, following the scenario that accretion flows sweep and accumulate H i gas to form molecular clouds.We follow the physical evolution of post-shock materials using a one-dimensional shock model, combined with post-processing gasice chemistry simulations. This approach allows us to study the evolution of the OPR(H 2 ) and water deuteration ratio without an arbitrary assumption of the initial molecular abundances, including the initial OPR(H 2 ). When the conversion of hydrogen into H 2 is almost complete the OPR(H 2 ) is already much smaller than the statistical value of three because of the spin conversion in the gas phase. As the gas accumulates, the OPR(H 2 ) decreases in a non-equilibrium manner. We find that water ice can be deuterium-poor at the end of its main formation stage in the cloud, compared to water vapor observed in the vicinity of low-mass protostars where water ice is sublimated. If this is the case, the enrichment of deuterium in water should mostly occur at somewhat later evolutionary stages of star formation, i.e., cold prestellar/protostellar cores. The main mechanism to suppress water ice deuteration in the cloud is the cycle of photodissociation and reformation of water ice, which efficiently removes deuterium from water ice chemistry. The removal efficiency depends on the main formation pathway of water ice. The OPR(H 2 ) plays a minor role in water ice deuteration at the main formation stage of water ice.

As a part of the Herschel key programme PRISMAS, we have used the Herschel/HIFI instrument to observe interstellar nitrogen hydrides along the sight-lines towards eight high-mass star-forming regions in order to elucidate the production pathways leading to nitrogen-bearing species in diffuse gas. Here, we report observations towards W49N of the NH N = 1-0, J = 2-1, and J = 1-0, ortho-NH 2 N Ka,Kc J = 1 1,1 3/2-0 0,0 1/2, ortho-NH 3 J K = 1 0 -0 0 and 2 0 -1 0 , para-NH 3 J K = 2 1 -1 1 transitions, and unsuccessful searches for NH + . All detections show absorption by foreground material over a wide range of velocities, as well as absorption associated directly with the hot-core source itself. As in the previously published observations towards G10.6−0.4, the NH, NH 2 and NH 3 spectra towards W49N show strikingly similar and non-saturated absorption features. We decompose the absorption of the foreground material towards W49N into different velocity components in order to investigate whether the relative abundances vary among the velocity components, and, in addition, we re-analyse the absorption lines towards G10.6−0.4 in the same manner. Abundances, with respect to molecular hydrogen, in each velocity component are estimated using CH, which is found to correlate with H 2 in the solar neighbourhood diffuse gas. The analysis points to a co-existence of the nitrogen hydrides in diffuse or translucent interstellar gas with a high molecular fraction. Towards both sources, we find that NH is always at least as abundant as both o-NH 2 and o-NH 3 , in sharp contrast to previous results for dark clouds. We find relatively constant N(NH)/N(o-NH 3 ) and N(o-NH 2 )/N(o-NH 3 ) ratios with mean values of 3.2 and 1.9 towards W49N, and 5.4 and 2.2 towards G10.6−0.4, respectively. The mean abundance of o-NH 3 is ∼2 × 10 −9 towards both sources. The nitrogen hydrides also show linear correlations with CN and HNC towards both sources, and looser correlations with CH. The upper limits on the NH + abundance indicate column densities 2-14% of N(NH), which is in contrast to the behaviour of the abundances of CH + and OH + relative to the values determined for the corresponding neutrals CH and OH. Surprisingly low values of the ammonia ortho-to-para ratio are found in both sources, ≈0.5-0.7 ± 0.1, in the strongest absorption components. This result cannot be explained by current models as we had expected to find a value of unity or higher.

No abstract

We have used the Herschel-HIFI instrument to observe the two nuclear spin symmetries of amidogen (NH 2 ) towards the high-mass star-forming regions W31C (G10.6−0.4), W49N (G43.2−0.1), W51 (G49.5−0.4), and G34.3+0.1. The aim is to investigate the ratio of nuclear spin types, the ortho-to-para ratio (OPR) of NH 2 in the translucent interstellar gas, where it is traced by the line-of-sight absorption, and in the envelopes that surround the hot cores. The HIFI instrument allows spectrally resolved observations of NH 2 that show a complicated pattern of hyperfine structure components in all its rotational transitions. The excited NH 2 transitions were used to construct radiative transfer models of the hot cores and surrounding envelopes to investigate the excitation and possible emission of the ground-state rotational transitions of ortho-NH 2 N Ka,Kc J = 1 1,1 3/2-0 0,0 1/2 (953 GHz) and para-NH 2 2 1,2 5/2-1 0,1 3/2 (1444 GHz) used in the OPR calculations. Our best estimate of the average OPR in the envelopes lie above the high-temperature limit of three for W49N, specifically 3.5 with formal errors of ±0.1, but for W31C, W51, and G34.3+0.1 we find lower values of 2.5 ± 0.1, 2.7 ± 0.1, and 2.3 ± 0.1, respectively. Values this low are strictly forbidden in thermodynamical equilibrium since the OPR is expected to increase above three at low temperatures. In the translucent interstellar gas towards W31C, where the excitation effects are low, we find similar values between 2.2 ± 0.2 and 2.9 ± 0.2. In contrast, we find an OPR of 3.4 ± 0.1 in the dense and cold filament connected to W51 and also two lower limits of 4.2 and 5.0 in two other translucent gas components towards W31C and W49N. At low temperatures (T 50 K) the OPR of H 2 is <10 −1 , far lower than the terrestrial laboratory normal value of three. In this para-enriched H 2 gas, our astrochemical models can reproduce the variations of the observed OPR, both below and above the thermodynamical equilibrium value, by considering nuclear-spin gas-phase chemistry. The models suggest that values below three arise in regions with temperatures 20−25 K, depending on time, and values above three at lower temperatures.