Water and some organic molecules were found to be deuterium enriched toward various astronomical targets. Understanding the deuterium-fractionation process pertains directly to know how and when molecules are created. Although gas phase chemistry is certainly important for deuterium enrichment, the role of physicochemical processes on the dust surfaces should be also considered. In fact, the extreme deuterium enrichment of formaldehyde and methanol requires the dust grain-surface process. In this context, we have performed a series of experiments on the formation of deuterated species of water and simple organic molecules. From the results of these experiments and related works, I will discuss the key processes for the deuterium enrichment on dust. For deuterium chemistry, another important issue is the ortho-to-para ratio (OPR) of H₂, which is closely related to the formation of H₂D⁺ and thus the deuterium fractionation of molecules in the gas phase. Because the radiative nuclear spin conversion of H₂ is forbidden, the ortho-para conversion is very slow in the gas phase. In contrast, it was not obvious how the nuclear spins behave on cosmic dust. Therefore, it is desirable to understand how the OPR of H₂ is determined on the dust surfaces. We have tackled this issue experimentally. Using experimental techniques of molecular beam, photostimulated-desorption, and resonance-enhanced multiphoton ionization, we measured the OPRs of H₂ photodesorbed from amorphous solid water at around 10 K, which is an ice dust analogue. It was first demonstrated that the rate of spin conversion from ortho to para drastically increases from 2.4 × 10⁻⁴ to 1.7 × 10⁻³ s⁻¹ within the very narrow temperature window of 9.2 to16 K. The observed strong temperature cannot be explained by solely state-mixing models ever proposed but by the energy dissipation model via two phonon process. I will present our recent experiments regarding this.

Protostars form from cold dense cores dominated by molecular gas and dust, showing excess continuum and rich spectra beyond 100 μm that are best observed by Herschel Space Observatory. Molecular emission reveals the properties of the surrounding gas and the underlying physical processes that govern the early stage of star formation. The CO in Protostars (COPS) Herschel program observes 27 embedded protostars with SPIRE, including several dominant molecular species, such as CO, ¹³CO, H₂O, and HCO⁺. The COPS dataset covers a unique wavelength range, allowing us to investigate the early stage of star formation across a large sample of sources. We detect CO rotational lines from J_up = 4 to 36, ¹³CO lines from J_up = 5 to 10, and six H₂O lines, along with [N  II] and [C  I]. We have created an uniformly calibrated dataset with the data from Dust, Ice, and Gas In Time (DIGIT) Herschel Key Program and archival photometry, in which we characterize each source by its spectral energy distribution and evolutionary class. With an automatic line fitting pipeline, we detect 323 lines from 25 sources from which we successfully extracted 1D spectra, and 3068 lines from 27 sources observed in all spatial pixels of SPIRE. We analyze the correlations of the line strengths of every line pair from all lines detected with two methods from ASURV package, Spearman's ρ, which test whether the line strengths relation can be described by a monotonic function, and the Kendall z-value, which quantifies the similarity of the ordering of the line strengths of two lines. The distribution of correlations shows a systematic tendency coinciding with the wavelength coverages of the instruments, suggesting that the correlations should only be compared within the lines observed by each module. Within each module, the correlations of two CO line pairs show high correlations, which decrease as the difference of the upper J-level of the two CO lines increases. The smooth gradients of the distribution of correlations hint that the temperature and density of CO gas are continuously varying throughout the embedding envelope. If all CO gas in the envelope shares a same temperature or density, the correlations would be strong for two CO lines originating from two very different J-levels. We find no obvious clustering in the distribution of correlations, while a group of CO lines could have shown particularly strong correlations if their properties were dominated by a same physical process.

The atomic to molecular transitions occurring in diffuse interstellar gas surrounding molecular clouds are affected by the local physical conditions (density and temperature) and the radiation field penetrating the material. Our optical observations of CH, CH⁺, and CN absorption from McDonald Observatory and the European Southern Observatory are useful tracers of this gas and provide the velocity structure needed for analyzing lower resolution ultraviolet observations of CO and H₂ absorption from Far Ultraviolet Spectroscopic Explorer. We explore the changing environment between diffuse and dense gas by using the column densities and excitation temperatures from CO and H₂ to determine the gas density. The resulting gas densities from this method are compared to densities inferred from other methods such as C₂ and CN chemistry. The densities allow us to interpret the trends from the combined set of tracers. Groupings of sight lines, such as those toward h and χ Persei or Chameleon provide a chance for further characterization of the environment. The Chameleon region in particular helps illuminate CO-dark gas, which is not associated with emission from H I at 21 cm or from CO at 2.6 mm. Expanding this analysis to include emission data from the GOT C+ survey allows the further characterization of neutral diffuse gas, including CO-dark gas.

In the last few decades sulfur bearing molecules have become a relevant topic in astrochemistry. The observed overall abundances of these compounds in the dense gas and around young stellar objects is indeed not in agreement with the estimated cosmic abundance of sulfur (Tieftrunk et al. 1994; Palumbo et al. 1997). Many studies point to polysulphanes and sulphur polymers, mainly S₈, as possible sulfur reservoirs, which from solid phase might be released into gas phase as simpler sulfur compounds, e.g. in shocked or hot environments (Wakelam et al. 2004; Laas, in prep.). Laboratory studies on dust and ice analogues indicate CS₂ as a potential decomposition product of the sulfur residue (Jiménez-Escobar et al. 2014 and references therein). Nevertheless, this species is not detectable by radio-telescopes due to lack of permanent dipole moment. Dithioformic acid (HCSSH), a possible byproduct of interstellar CS₂, may thus serve as a proxy for this non-polar S-bearing molecule. Millimeter and sub-millimeter spectra have been recorded and analyzed for the trans and cis conformers of HCSSH, up to 478 GHz. We employed the frequency modulation sub-millimeter absorption spectrometer recently developed at the Center for Astrochemical Studies (CAS) in Garching. HCSSH was produced by a glow discharge mixture of CS₂ and H₂ diluted in Ar. Accurate rest frequencies, which might serve as guidance for astronomical searches have been obtained thanks to our recent experiment. In particular trans-HCSSH, the lowest-energy conformer, is the best candidate for a potential detection.

The number of unidentified lines in the millimeter and submillimeter wave surveys of the interstellar medium has grown rapidly. The major contributions are due to rotational transitions in excited vibrational states of a relatively few molecules that are called the astrophysical weeds Fortman, S. M., Medvedev, I. R., Neese, C.F., & De Lucia, F.C. 2010, ApJ,725, 1682^, Rotational Spectra in 29 Vibrationally Excited States of Interstellar Aminoacetonitrile, L. Kolesnikov, E. R. Alonso, S. Mata, and J. L. Alonso, The Astrophysical Journal Supplement Series 2017, (in press)..

In regions of star formation, astrophysical shocks have been found to be both common and influential on the molecular make-up of the surrounding material. The formation of complex organic molecules (COMs) in the interstellar medium relies on interplay between gas-phase and grain-surface physical and chemical processes, including shock-induced non-thermal desorption of COMs formed on the grain. We will utilize the gas-grain chemical network model NAUTILUS, coupled with the inclusion of a high-temperature network and a parametric shock model, with the inclusion of collisional dust heating and sputtering processes from gas-phase particles, in order to study the effects shocks have on the chemical complexity of a prototypical shocked outflow over a range of chemically-relevant timescales. Here, we will present the effectiveness of using chemical tracers to determine the presence of a shock long after it has passed, as well as the prominence of post-shock gas-phase formation and destruction of shock-tracing molecules.

We present ALMA Cycle 2 observations of SiO(5-4) outflows towards 30 Infrared Dark Cloud (IRDC) clumps, which are spatially resolved down to  ∼ 0.05pc. Out of the 30 clumps observed, we have detected SiO emission in 20 clumps. We discuss the association of SiO with mm continuum and FIR emission, and fit the SEDs of potential protostellar sources with radiative transfer models based on the Turbulent Core Model. In 6 of the 20 clumps the SiO emission is stronger than the 10 sigma noise level and appears to trace outflows being driven by protostellar sources that are also revealed as nearby mm continuum peaks. We locate the dense protostellar cores associated with the outflows in position-velocity space utilizing dense gas tracers DCN(3-2), DCO⁺(3-2) and C¹⁸O(2-1). The different morphology and kinematics of the outflows indicate different core structures, accretion histories and ambient cloud environments. The mass and energetics of the outflows indicate that these 6 protostars are in a relatively early evolutionary stage and some may eventually become massive stars.

Maser observations of both linear and circular emission have provided unique information on the magnetic field in the densest regions of star forming regions. While linear polarization observations provide morphological constraints, the magnetic field strength determination is done by comparing the Zeeman-induced velocity shifts between left- and right-circularly polarized emission of molecular maser species. Soon, full-polarization observations with be possible with ALMA, making magnetic field measurements with unprecedented spatial resolution possible. In particular, methanol is of special interest as it is the most abundant maser species and its different transitions probe unique areas of high-mass proto-stellar disks and outflows. However, its exact Zeeman-parameters are unknown. Experimental efforts to determine the Zeeman-parameters have failed. Here we present quantum chemical calculations to the Zeeman-parameters of methanol, along with calculations to the hyperfine structure, which are also necessary to interpret the Zeeman effect in methanol. We present the proper treatment of the torsional motion in computing hyperfine and Zeeman effects. Our results on the hyperfine structure show good agreement with recent experimental data. We find that the Zeeman-effect in methanol is non-linear and comment on its applicability in astronomical magnetic field studies. We give an outlook on rigorously treating non-linear Zeeman effects in radiative transfer modeling of maser-species interacting with a magnetic field.

Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challenging due to the high sensitivity and high spectral resolution required. So far, the Zeeman effect has been detected unambiguously in star forming regions for very few non-masing species, such as OH and CN. We decided to investigate the ability of sulfur monoxide (SO), which is one of the most abundant species in star forming regions, for probing the intensity of magnetic fields via Zeeman effect. The Zeeman effect for several rotational transitions of SO in the (sub-)mm spectral regions has been investigated by using a frequency-modulated, computer-controlled spectrometer, and by applying a magnetic field parallel to the radiation source. To support the experimental determination of the g factors of SO, a systematic quantum-chemical investigation of these parameters for both SO and O₂ has been carried out. An effective experimental-computational strategy for providing accurate g factors as well as for identifying the rotational transitions showing the strongest Zeeman effect has been presented. Our investigation supports SO as a good candidate for probing magnetic fields in high-density star forming regions.

The role of magnetic fields in star formation remains controversial. Observations of the Zeeman effect provide the only available technique for directly measuring the strengths of magnetic fields in molecular clouds. We have mapped the Zeeman effect toward the massive star forming complex W3OH in the CN N=2-1 transition at 226 GHz with both the IRAM 30-m telescope and the CARMA array and have combined these data to produce a fully spatially sampled map of the magnetic field along the line of sight, with approximately 4 arcsec resolution. These are both the first CN Zeeman maps and the first detections of the Zeeman effect in the CN N=2-1 transition. We will present this map and discuss the astrophysical implications. This work may be considered to be a pathfinder for future similar ALMA observations, which have the potential to advance considerably our understanding of the role of magnetic fields in the star formation process.

Magnetic fields are a crucial element of the star formation process on many scales, from controlling jet and outflow formation on large scales, determining the structure of any protostellar disk, to modulating the accretion rate onto the central protostar. Both the three-dimensional structure and the field strength are important in determining the outcome of star formation. Unfortunately, the method most commonly used to infer magnetic field structure - linearly polarized dust continuum emission - is limited to the plane-of-sky field structure, and gives no reliable information on field strength. Alternatively, observations of the Zeeman effect in transitions of paramagnetic molecules, especially CN, are one of the best prospects for making such measurements due to the molecules' high Zeeman coefficients. In particular, these observations have been used in determining field strengths on cloud-size scales. However, CN and other paramagnetic molecules have, to our knowledge, never been observed in the envelopes/disks of Class 0 protostars at  ∼ arcsecond resolution, due both to sensitivity and resolution limits of previous generations of millimeter-wave interferometers. Because field strengths near the protostar are so important to understand the star formation process, we have conducted a snapshot ALMA Band 3 (3 mm / 113 GHz) survey of the 10 brightest Class 0 protostars in the Perseus, Taurus, and ρ Ophiuchus molecular clouds in the regions surrounding five transitions of four paramagnetic species, including CN, SO, C₂S, and C₄H. We present this survey - the principle goal of which was to assess the brightness of the lines within  ∼  1000 AU of the protostar - and assess the likelihood of using ALMA observations of the Zeeman effect to determine protostellar magnetic field strength.