We present a comprehensive analysis of a broad band spectral line survey of the Orion Kleinmann-Low nebula (Orion KL), one of the most chemically rich regions in the Galaxy, using the HIFI instrument on board the Herschel Space Observatory. This survey spans a frequency range from 480 to 1907 GHz at a resolution of 1.1 MHz. These observations thus encompass the largest spectral coverage ever obtained toward this high-mass star-forming region in the sub-mm with high spectral resolution, and include frequencies > 1 THz where the Earth's atmosphere prevents observations from the ground. In all, we detect emission from 39 molecules (79 isotopologues). Combining this dataset with ground based mm spectroscopy obtained with the IRAM 30 m telescope, we model the molecular emission from the mm to the far-IR using the XCLASS program which assumes local thermodynamic equilibrium (LTE). Several molecules are also modeled with the MADEX non-LTE code. Because of the wide frequency coverage, our models are constrained by transitions over an unprecedented range

Context. We present a study of the sulphur chemistry evolution in the region Orion KL along the gas and grain phases of the cloud. Aims. Our aim is to investigate the processes that dominate the sulphur chemistry in Orion KL and to determine how physical and chemical parameters, such as the final mass of the star and the initial elemental abundances, influence the evolution of the hot core and of the surrounding outflows and shocked gas (the plateau). Methods. We independently modelled the chemistry evolution of the hot core and the plateau using the time-dependent gas-grain model UCL_CHEM and considering two different phase calculations. Phase I starts with the collapsing cloud and the depletion of atoms and molecules onto grain surfaces. Phase II starts when a central protostar is formed and the evaporation from grains takes place. We show how the stellar mass, the gas density, the gas depletion efficiency, the initial sulphur abundance, the shocked gas temperature, and the different chemical paths on the grains leading to different reservoirs of sulphur on the mantles affect sulphurbearing molecules at different evolutionary stages for both components. We also compare the predicted column densities with those inferred from observations of the species SO, SO 2 , CS, OCS, H 2 S, and H 2 CS.Results. The models that reproduce the observations of the largest number of sulphur-bearing species in both components are those with an initial sulphur abundance of 0.1 times the sulphur solar abundance (0.1 S ) and a density of at least n H = 5 × 10 6 cm −3 in the shocked gas region. Conclusions. We conclude that most of the sulphur atoms were ionised during Phase I, consistent with an inhomogeneous and clumpy region where the UV interstellar radiation penetrates and leading to sulphur ionisation. We also conclude that the main sulphur reservoir on the ice mantles was H 2 S. In addition, we deduce that a chemical transition currently takes place in the plateau shocked gas, where SO and SO 2 gas-phase formation reactions change from being dominated by O 2 to being dominated by OH.

Context. We present a study of the sulfur-bearing species detected in a line confusion-limited survey towards Orion KL performed with the IRAM 30-m telescope in the frequency range 80−281 GHz. Aims. This study is part of an analysis of the line survey divided into families of molecules. Our aim is to derive accurate physical conditions, as well as molecular abundances, in the different components of Orion KL from observed SO and SO 2 lines. Methods. As a starting point, we assumed local thermodynamic equilibrium (LTE) conditions obtain rotational temperatures. We then used a radiative transfer model, assuming either LVG or LTE excitation to derive column densities of these molecules in the different components of Orion KL. = 1 and for several undetected sulfur-bearing species. In addition, we present 2 × 2 maps around Orion IRc2 of SO 2 transitions with energies from 19 to 131 K and also maps with four transitions of SO, 34 SO, and 34 SO 2 . We observe an elongation of the gas along the NE-SW direction. An unexpected emission peak appears at 20.5 km s −1 in most lines of SO and SO 2 . A study of the spatial distribution of this emission feature shows that it is a new component of a few arcseconds (∼5 ) in diameter, which lies ∼4 west of IRc2. We suggest the emission from this feature is related to shocks associated to the BN object. Conclusions. The highest column densities for SO and SO 2 are found in the high-velocity plateau (a region dominated by shocks) and in the hot core. These values are up to three orders of magnitude higher than the results for the ridge components. We also find high column densities for their isotopologues in both components. Therefore, we conclude that SO and SO 2 are good tracers, not only of regions affected by shocks, but also of regions with warm dense gas (hot cores).

Context. The presence of dust can strongly affect the chemical composition of the interstellar medium. We model the chemistry in photodissociation regions (PDRs) using both gas-phase and dust-phase chemical reactions. Aims. Our aim is to determine the chemical compositions of the interstellar medium (gas/dust/ice) in regions with distinct (molecular) gas densities that are exposed to radiation fields with different intensities. Methods. We have significantly improved the Meijerink PDR code by including 3050 new gas-phase chemical reactions and also by implementing surface chemistry. In particular, we have included 117 chemical reactions occurring on grain surfaces covering different processes, such as adsorption, thermal desorption, chemical desorption, two-body reactions, photo processes, and cosmicray processes on dust grains. Results. We obtain abundances for different gas and solid species as a function of visual extinction, depending on the density and radiation field. We also analyse the rates of the formation of CO 2 and H 2 O ices in different environments. In addition, we study how chemistry is affected by the presence/absence of ice mantles (bare dust or icy dust) and the impact of considering different desorption probabilities. Conclusions. The type of substrate (bare dust or icy dust) and the probability of desorption can significantly alter the chemistry occurring on grain surfaces, leading to differences of several orders of magnitude in the abundances of gas-phase species, such as CO, H 2 CO, and CH 3 OH. The type of substrate, together with the density and intensity of the radiation field, also determine the threshold extinction to form ices of CO 2 and H 2 O. We also conclude that H 2 CO and CH 3 OH are mainly released into the gas phase of low, far-ultraviolet illuminated PDRs through chemical desorption upon two-body surface reactions, rather than through photodesorption.

Context. We present a study of cyanoacetylene (HC 3 N) and cyanodiacetylene (HC 5 N) in Orion KL using observations from two line surveys performed with the IRAM 30-m telescope and the HIFI instrument onboard the Herschel telescope. The frequency ranges covered are 80−280 GHz and 480−1906 GHz. Aims. This study (divided by families of molecules) is part of a global analysis of the physical conditions of Orion KL and the molecular abundances in the different components of this cloud. Methods. We modeled the observed lines of HC 3 N, HC 5 N, their isotopologues (including DC 3 N), and vibrational modes using a non-local thermodynamic equilibrium (non-LTE) radiative transfer code. In addition, to investigate the chemical origin of HC 3 N and DC 3 N in Orion KL, we used a time-dependent chemical model. Results. We detect 40 lines of the ground vibrational state of HC 3 N and 68 lines of its 13 C isotopologues. We also detect 297 lines of six vibrational modes of this molecule (ν 7 , 2ν 7 , 3ν 7 , ν 6 , ν 5 , and ν 6 +ν 7 ) and 35 rotational lines of the ground vibrational state of HC 5 N. We report the first tentative detection of DC 3 N in a giant molecular cloud. We have obtained a DC 3 N/HC 3 N abundance ratio of 0.015 ± 0.009, similar to typical D/H ratios of cold dark clouds. We provide column densities for all species and derived isotopic and molecular abundances. We also made a 2 × 2 map around Orion IRc2 and present maps of the HC 3 N lines with energies from 34 to 154 K and of the HC 3 N vibrational modes ν 6 and ν 7 with energies between 354 and 872 K. In addition, a comparison of our results for HC 3 N with those in other clouds has allowed us to derive correlations between the column density, the FWHM, the mass, and the luminosity of the clouds. Conclusions. The high column densities of HC 3 N obtained in the hot core, in particular of the ground vibrational state and the vibrational mode ν 7 , make this molecule an excellent tracer of hot and dense gas. In addition, the wide frequency range covered reveals the need to consider a temperature and density gradient in the hot core to obtain better line fits. The high D/H ratio (similar to that obtained in cold clouds) that we derive suggests a deuterium enrichment. Our chemical models indicate that the possible deuterated HC 3 N in Orion KL is formed during the gas-phase. This fact provides new hints concerning the processes leading to deuteration.