Methyl cyanide, CH_3CN, is present in diverse regions in space, in particular in the warm parts of star-forming regions where it is a common molecule. Rotational transitions of ^13CH_3CN and CH_3^13CN in their v_8 = 1 lowest excited vibrational states (E_ vib≈ 520 K) are quite prominent in Sagittarius B2(N). In order to be able to search for transitions of the next higher vibrational state v_8 = 2, we recorded spectra of samples enriched in ^13CH_3CN and CH_3^13CN up to v_8 = 2 in the 35 to 1091 GHz region and reinvestigated existing spectra of CH_3CN in its natural isotopic composition between 1085 and 1200 GHz. Perturbations caused by near-degeneracies in K = 4 of v_8 = 2^0 and K = 2 of v_8 = 2^-2 yielded accurate information on the energy spacing of 22.93 and 21.79 cm^-1 between the l-components of ^13CH_3CN and CH_3^13CN, respectively. Fermi-type interaction between K = 13 and 14 of v_8 = 1^-1 and v_8 = 2^+2 probe the energy differences between the two states of both isotopomers. In addition, a ΔK ±2, Δl ∓1 interaction between the ground vibrational state of ^13CH_3CN and v_8 = 1^+1 provides information on their energy spacing. Furthermore, we obtained improved or extended ground state rotational transition frequencies of ^13CH_3^13CN and extensive data for ^13CH_3C^15N and CH_3^13C^15N. Finally, we report the results of our search for transitions of ^13CH_3CN and CH_3^13CN in their v_8 = 2 states toward Sagittarius B2(N).

Sulfur is one of the most abundant elements in the interstellar medium (ISM) and a key component for life, yet little is understood about its chemistry in the ISM. While increasingly larger molecules containing sulfur and oxygen are being observed in the ISM, the largest organic molecule containing oxygen and sulfur, monothioformic acid (HC(O)SH), was only recently detected. There is still no identification of a complex organic molecule (COM, carbon-bearing molecule with six or more atoms) containing both oxygen- and sulfur-bearing functional groups. We extended the laboratory rotational spectrum of 2-mercaptoethanol (HSCH2CH2OH), one of the simplest saturated COMs containing both oxygen and sulfur, into millimeter/submillimeter wavelengths, providing an improved spectral catalog at frequencies required for its interstellar identification. Millimeter/submillimeter transitions were measured for 2-mercaptoethanol from similar to 82 to 450 GHz. Using the resulting spectral catalog, we searched for its rotational emission toward the Galactic Center molecular cloud G+0.693-0.027, the high-mass star-forming region Sgr B2(N), the cold dark core TMC-1, the hot core in Orion, and toward the hot corino surrounding the low-mass protostar IRAS 16293-2422B. An extensive analysis of 8584 transitions of 2-mercaptoethanol with Jmax '' = 104, and Kamax '' = 64 is provided. The resulting fit includes a full set of quartic, sextic, and octic distortion constants. We report the nondetection of 2-mercaptoethanol and provide column density upper limits toward each source. While our interstellar search for 2-mercaptoethanol did not result in a detection, the upper limits on its column density provide important constraints for chemical models on the formation of oxygen- and sulfur-bearing COMs.

This document contains the supplementary materials (Appendix B, C, and D) of the paper 'Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). V. Tracing cavity walls and shocked knots with non-thermally desorbed CH3OH in BHR71-IRS1'.

Context. Many complex organic molecules (COMs) in star-forming regions are believed to form on dust grains. We thus expect both the reduced metallicity and dust-to-gas ratio in the outer Galaxy to have an impact on the chemical composition of these regions. Aims. We investigate if certain COMs are more sensitive than others to metallicity by measuring the chemical composition of hot cores in the outer Galaxy. Methods. We used the interferometer NOEMA to perform an imaging spectral line survey of G135.27+2.79, a hot core candidate located at a galactocentric distance of 13.1 kpc. We derived the rotational temperatures and column densities of the detected molecules while assuming local thermodynamic equilibrium and compared the chemical composition of G135.27+2.79 to other sources and to the predictions of the three-phase astrochemical code MAGICKAL. Results. G135.27+2.79 hosts three continuum cores, labeled MM1, MM2, and MM3. Toward MM1, we detected 28 molecules, including 12 COMs, and several of their less abundant isotopologs. Most species trace a hot, compact region, confirming MM1 as a hot core (the third one identified in the outer Galaxy). MM1 drives a bipolar CO outflow. COMs show a velocity gradient along the outflow axis but opposite to that of CO, which may be related to a wide-angle disk wind. The chemical composition of MM1 correlates rather well with that of the inner and outer Galaxy hot cores G31.41+0.31 and WB89-789 SMM1, but its molecular abundances relative to methanol lie in between, which may reflect the influence of metallicity on COM formation. The model results agree reasonably well, though with a few notable exceptions, with the COM abundances of MM1 relative to methanol and with the abundance ratios between MM1 and G31.41+0.31. Sensitivity to the reduced metallicity and dust-to-gas ratio varies between molecules, with carbon chains and nitriles most negatively affected. The lower dust-to-gas ratio leads to slower adsorption under low-metallicity conditions so that more carbon is locked up into CO in the gas. Slow adsorption means that CO is hydrogenated more efficiently on grains, enhancing CO-related COM abundances above expectations. Conclusions. These results demonstrate that metallicity has a significant impact on the formation of COMs. A larger source sample is needed to investigate the robustness of the deviations noted between the model and the observations for a few species.

Methyl cyanide, CH3CN, is present in diverse regions in space, in particular in the warm parts of star-forming regions where it is a common molecule. Rotational transitions of 13CH3CN and CH3 13CN in their v 8 = 1 lowest excited vibrational states (E vib approximate to 520 K) are quite prominent in Sagittarius B2(N). In order to be able to search for transitions of the next higher vibrational state v 8 = 2, we recorded spectra of samples enriched in 13CH3CN and CH3 13CN up to v 8 = 2 in the 35-1091 GHz region and reinvestigated existing spectra of CH3CN in its natural isotopic composition between 1085 and 1200 GHz. Perturbations caused by near-degeneracies in K = 4 of v 8 = 20 and K = 2 of v 8 = 2-2 yielded accurate information on the energy spacing of 22.93 and 21.79 cm-1 between the l components of 13CH3CN and CH3 13CN, respectively. Fermi-type interaction between K = 13 and 14 of v 8 = 1-1 and v 8 = 2+2 probe the energy differences between the two states of both isotopomers. In addition, a Delta K +/- 2, Delta l -/+ 1 interaction between the ground vibrational state of 13CH3CN and v 8 = 1+1 provides information on their energy spacing. Furthermore, we obtained improved or extended ground-state rotational transition frequencies of 13CH3 13CN and extensive data for 13CH3C15N and CH3 13C15N. Finally, we report the results of our search for transitions of 13CH3CN and CH3 13CN in their v 8 = 2 states toward Sagittarius B2(N).

Despite the detection of nearly 350 molecules in the interstellar medium, almost half of which are carbon chains, the pathways that build molecular complexity remain poorly understood. Observed abundances of carbon-chain and aromatic species are difficult to reconcile with existing top-down or bottom-up formation scenarios, due in part to limited observational constraints and incomplete theoretical understanding. In particular, small intermediary ions, key drivers of ion-molecule reactions capable of seeding larger hydrocarbons and aromatic rings, could provide critical support for the bottom-up formation scenario. Constraining the abundance and chemistry of these ions is therefore essential to test whether bottom-up growth can operate efficiently under interstellar conditions. Here, we report the first detection of the small hydrocarbon cation ethynylium, C2H+, toward the Orion Bar, based on observations with the APEX 12m sub-mm telescope of its lowest-lying J=3-2 rotational transition near 211GHz, which exhibits a unique spectroscopic fingerprint through resolved Lambda-doubling and hyperfine splitting components, as recently measured in the laboratory. Meudon PDR models successfully reproduce these values, placing C2H+ formation at the outer edges of PDR fronts. Our results link C2H+ production to CH+ and CH3+ within a network of ion-molecule reactions driven by vibrationally excited H2, a scenario now further supported by recent detections of these species in PDRs like the Orion Bar with JWST observations. The importance of C2H+ lies in its role as a key intermediate: it produces C2H2+ and subsequently C2H3+, effectively channelling small C2 building blocks toward larger hydrocarbons and facilitating bottom-up growth at the PDR surface. Targeted searches for C2H+ in other regions promise to provide a potentially decisive probe of ion-driven bottom-up chemistry in the ISM.

Broadband measurements of glycidaldehyde in the frequency ranges 75-170 and 500-750 GHz were recorded to extend previous analyses of its pure rotational spectrum in the microwave region. The rotational parameters of the ground vibrational states for the main isotopologue and the three singly 13C-substituted isotopologues were considerably improved, and additional higher-order parameters were determined. To identify new vibrationally excited states in the dense and convoluted spectrum, an updated version of the double-modulation double-resonance spectroscopy technique was used. Connecting transitions with a shared energy level into series and expanding these via Loomis-Wood plots proved to be a powerful method, which allowed the identification of 11 new vibrationally excited states in addition to the already known aldehyde torsions, v21 = 1 to v21 = 6. Interactions between several vibrational states were observed, and three interacting systems were treated successfully. Rotational transitions of glycidaldehyde were searched for in the imaging spectral line survey ReMoCA obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming region Sgr B2(N). The observed spectra were modeled under the assumption of local thermodynamic equilibrium (LTE). Glycidaldehyde, an oxirane derivative, was not detected toward Sgr B2(N2b). The upper limit on its column density implies that it is at least six times less abundant than oxirane in this source.

We present an analysis of the millimeter-wave spectra of 2-aminopropenenitrile ( H 2 C = C ( NH 2 ) CN ), an α -aminonitrile of plausible prebiotic and astrophysical relevance. The molecule has a rotational spectrum that is in harmony with a large-amplitude motion of the amino group. Accurate rest transition frequencies are reported in selected regions between 158 and 324 GHz, along with extended and improved sets of molecular parameters for the ground state. In addition, several vibrational satellites were identified for the first time. Experimental results were used to search for 2-aminopropenenitrile toward two chemically rich interstellar sources in the Sgr B2 region of the Galactic center: the hot molecular core Sgr B2(N1S) and the molecular cloud G+0.693–0.027. We also searched for the reduced derivative, 2-aminopropionitrile ( CH 3 CH ( NH 2 ) CN ), in the former source. None of the molecules were detected, and the upper limits of their column densities were obtained.

We present an analysis of the millimeter-wave spectra of 2-aminopropenenitrile ( ${{\rm{H}}}_{2}{\rm{C}}\rm{=}{\rm{C}}({\mathrm{NH}}_{2})\mathrm{CN}$ ), an α -aminonitrile of plausible prebiotic and astrophysical relevance. The molecule has a rotational spectrum that is in harmony with a large-amplitude motion of the amino group. Accurate rest transition frequencies are reported in selected regions between 158 and 324 GHz, along with extended and improved sets of molecular parameters for the ground state. In addition, several vibrational satellites were identified for the first time. Experimental results were used to search for 2-aminopropenenitrile toward two chemically rich interstellar sources in the Sgr B2 region of the Galactic center: the hot molecular core Sgr B2(N1S) and the molecular cloud G+0.693–0.027. We also searched for the reduced derivative, 2-aminopropionitrile ( ${{\rm{CH}}}_{3}{\rm{CH}}({{\rm{NH}}}_{2}){\rm{CN}}$ ), in the former source. None of the molecules were detected, and the upper limits of their column densities were obtained.

We determined the ortho/para (o/p) ratios of NH2D and NHD2 in the archetypical pre-stellar core L1544. The core was observed in the two lowest rotational lines of ortho- and para-NH2D using the APEX and the IRAM 30 m telescopes. The ground-state lines of ortho- and para-NHD2 were observed with APEX. The distributions of chemical abundances in the core were predicted using a gas-grain chemistry model with two different scenarios concerning proton transfer reactions in the gas. One of the scenarios, the so-called full scrambling (FS), allows protons and deuterons to be completely mixed in the intermediate reaction complex before dissociation, whereas the other describes these reactions as proton or deuteron hops (PH). We also tested assumed abundance profiles independent of the chemistry models. Radiative transfer calculations were used to simulate the observed NH2D and NHD2 lines from the predicted and assumed abundance profiles. Our modelling efforts suggest that the ground-state lines of NH2D and NHD2 at the wavelength 0.9 mm that are observable with the same beam and in the same spectrometer band are the most reliable probes of the o/p ratios. Simulations using the PH reaction scheme show systematically better agreement with the observations than simulations with the FS model. Simulations using a broken power law abundance profile as a function of the gas density give spin ratios that are close to the predictions of the PH scenario: o/p-NH2D=2.85+-0.05, o/p-NHD2=2.10+-0.06 (1 sigma). The o/p ratios predicted by the PH scenario in the gas phase correspond to the nuclear spin statistical weights, that is, o/p-NH2D=3, o/p-NHD2=2. In view of the fact that H and D atom addition reactions on grain surfaces also result in these ratios, it is reasonable to assume that the spin ratios of interstellar ammonia and its deuterated forms are in general equal to their statistical values.

Thanks to the advent of sensitive and broad bandwidth instrumentation, complex organic molecules (COMs) have been found in a wide variety of interstellar environments, not only in our Galaxy but also in external galaxies up to a redshift of 0.89. The detection of COMs in cold environments such as starless or prestellar cores has challenged our understanding of COM formation and new ideas are being implemented in chemical models and explored in laboratory experiments. At the protostellar stage, the advent of new interferometers such as the Atacama Large Millimeter/submillimeter Array (ALMA) has allowed the mapping of the weak emission of COMs in the protostellar envelopes and protoplanetary disks around both low-mass and high-mass protostars, pinpointing their location and revealing differentiation between the different families of molecules. In this way, thermal and non-thermal desorption mechanisms can be probed, constraining the efficiency of formation of COMs in the gas phase versus on grain surfaces. Some degree of continuity in the COM composition is found from the early to late stages of star formation, suggesting that a significant fraction of COMs are formed at the initial conditions of star formation. For extreme environments such as the Galactic Center, cosmic rays and low-velocity shocks seem to influence the COM composition of low and high-density gas components. The spectral confusion limit will be a major challenge for the detection of new COMs in future spectroscopic surveys. However, low-frequency interferometers targeting sources with low-excitation temperatures may help to overcome this limit.

We report on large-scale radio observations of the Chamaeleon star-forming region obtained with the Australia Telescope Compact Array (ATCA) that led to the definite detection of five young stars and the tentative detection of five more. As in other regions surveyed in the radio domain, the majority of detected sources are fairly evolved low-mass T Tauri stars, but we also detect one protostellar object (Ced 110 IRS4) and one Herbig Ae/Be star. With the exception of the protostellar source, the radio emission mechanism is likely of non-thermal origin. The three brightest radio stars identified with ATCA were subsequently observed with the Australian Long Baseline Array (LBA) and one, J11061540-7721567 (Ced 110 IRS2), was detected at three epochs. This confirms the non-thermal nature of the radio emission in that specific case, and enabled accurate radio position measurements. Comparison with predictions from Gaia DR3 strongly suggests that this star is a binary system with an orbital period of order 40 years; additional LBA observations in the next decades would enable accurate determinations of the individual stellar masses in that system.

We synthesized the astrochemically relevant molecule 3-hydroxypropanal (HOCH _2 CH _2 CHO) and subsequently measured and analyzed its rotational spectrum in several frequency regions ranging from 130 to 485 GHz. We analyzed the ground vibrational state as well as the two perturbed lowest-lying vibrationally excited states. With the resulting rotational parameters, we searched for this molecule in the Sagittarius B2(N) and NGC 6334I hot cores, the IRAS 16293-2422B hot corino, and the G+0.693-0.027 and TMC-1 molecular clouds. Rotational emission of 3-hydroxypropanal was tentatively detected toward G+0.693-0.027, and a column density of (8.6 ±1.4) × 10 ^12 cm ^−2 was determined. However, this molecule was not detected in the other sources that were investigated. The chemical implications of this tentative discovery are analyzed, and several potential chemical formation pathways of this species are discussed.

Pre-stellar cores are the first steps in the process of star and planet formation. However, the dynamical and chemical evolution of pre-stellar cores is still not well understood. We aim at estimating the central density of the pre-stellar core IRAS16293E and at carrying out an inventory of molecular species towards the density peak of the core. We observed high-J rotational transitions of N_2H^+ and N_2D^+, and several other molecular lines towards the dust emission peak using the Atacama Pathfinder EXperiment (APEX) telescope, and derived the density and temperature profiles of the core using far-infrared surface brightness maps from Herschel. The N_2H^+ and N_2D^+ lines were analysed by non-LTE radiative transfer modelling. Our best-fit core model consists in a static inner region, embedded in an infalling envelope with an inner radius of approximately 3000 au (21" at 141 pc). The observed high-J lines of N_2H^+ and N_2D^+ (with critical densities greater than 10^6 cm^-3) turn out to be very sensitive to depletion; the present single-dish observations are best explained with no depletion of N_2H^+ and N_2D^+ in the inner core. The N_2D^+/N_2H^+ ratio that best reproduces our observations is 0.44, one of the largest observed to date in pre-stellar cores. Additionally, half of the molecules that we observed are deuterated isotopologues, confirming the high-level of deuteration towards this source. Non-LTE radiative transfer modelling of N_2H^+ and N_2D^+ lines proved to be an excellent diagnostic of the chemical structure and dynamics of a pre-stellar core. Probing the physical conditions immediately before the protostellar collapse is a necessary reference for theoretical studies and simulations with the aim of understanding the earliest stages of star and planet formation and the time scale of this process.

Context. Molecules containing two or more hydrogen or deuterium atoms have different nuclear spin states which behave as separate chemical species. The relative abundances of these species can give clues to their origin. Formation on grains is believed to yield statistical spin ratios whereas gas-phase reactions are predicted to result in clear deviations from them. This is also true for ammonia and its deuterated forms NH2D, NHD2, and ND3. Aims. Here we aim to determine the ortho/para ratios of NH2D and NHD2 in dense, starless cores, where their formation is supposed to be dominated by gas-phase reactions. Methods. The Large APEX sub-Millimeter Array (LAsMA) multibeam receiver of the Atacama Pathfinder EXperiment (APEX) telescope was used to observe the prestellar cores H-MM1 and Oph D in Ophiuchus in the ground-state lines of ortho and para NH2D and NHD2. The fractional abundances of these molecules were derived employing three-dimensional radiative transfer modelling, using different assumptions about the abundance profiles as functions of density. We also ran gas-grain chemistry models with different scenarios concerning proton or deuteron exchanges and chemical desorption from grains to find out if one of these models can reproduce the observed spin ratios. Results. The observationally deduced ortho/para ratios of NH2D and NHD2 are in both cores within 10% of their statistical values 3 and 2, respectively, and taking 3 σ limits, deviations from these of about 20% are allowed. Of the chemistry models tested here, the model that assumes proton hop (as opposed to full scrambling) in reactions contributing to ammonia formation, and a constant efficiency of chemical desorption, comes nearest to the observed abundances and spin ratios. Conclusions. The nuclear spin ratios derived here are in contrast with spin-state chemistry models that assume full scrambling in proton donation and hydrogen abstraction reactions leading to deuterated ammonia. The efficiency of chemical desorption strongly influences the predicted abundances of NH3, NH2D, and NHD2, but has a lesser effect on their ortho/para ratios. For these the proton exchange scenario in the gas is decisive. We suggest that this is because of rapid re-processing of ammonia and related cations by gas-phase ion-molecule reactions.

Context. IRAS 16293E is a rare case of a prestellar core being subjected to the effects of at least one outflow. Aims. We want to disentangle the actual structure of the core from the outflow impact and evaluate the evolutionary stage of the core. Methods. Prestellar cores being cold and depleted, the best tracers of their central regions are the two isotopologues of the trihydrogen cation that are observable from the ground: ortho-H2D+ and para-D2H+. We used the Atacama Pathfinder EXperiment (APEX) telescope to map the para-D2H+ emission in IRAS 16293E and collected James Clerk Maxwell Telescope (JCMT) archival data of ortho-H2D+. We compared their emission to that of other tracers, including dust emission, and analysed their abundance with the help of a 1D radiative transfer tool. The ratio of the abundances of ortho-H2D+ to para-D2H+ can be used to estimate the stage of the chemical evolution of the core. Results. We have obtained the first complete map of para-D2H+ emission in a prestellar core. We compare it to a map of ortho-H2D+ and show their partial anti-correlation. This reveals a strongly evolved core with a para-D2H+/ortho-H2D+ abundance ratio towards the centre for which we obtain a conservative lower limit from 3.9 (at 12 K) to 8.3 (at 8 K), while the high extinction of the core is indicative of a central temperature below 10 K. This ratio is higher than predicted by the known chemical models found in the literature. Para-D2H+ (and indirectly ortho-H2D+) is the only species that reveals the true centre of this core, while the emission of other molecular tracers and dust are biased by the temperature structure that results from the impact of the outflow. Conclusions. This study is an invitation to reconsider the analysis of previous observations of this source and possibly questions the validity of the deuteration chemical models or of the reaction and inelastic collisional rate coefficients of the H+3 isotopologue family. This could impact the deuteration clock predictions for all sources.

Context. Methanol is an abundant and widespread molecule in the interstellar medium. The column density of its O-18 isotopolog, (CH3OH)-O-18, is in some star-forming regions so high that the search for (CH3OH)-O-17 is promising. But only very few transition frequencies of CH317 OH with a microwave accuracy have been published prior to our investigation. Aims. We want to extend the very limited rotational line list of (CH3OH)-O-17 to be able to search for this isotopolog in the interstellar medium. Methods. We recorded the rotational spectrum of (CH3OH)-O-17 between 38 and 1095 GHz employing a methanol sample enriched in O-17 to 20%. A torsion-rotation Hamiltonian model based on the rho-axis method was employed to fit the data, as in our previous studies. We searched for rotational transitions of (CH3OH)-O-17 in the imaging spectral line survey ReMoCA obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming region Sgr B2(N). The observed spectra were modeled under the assumption of local thermodynamic equilibrium (LTE). Results. The assignments cover 0 <= J <= 45, K-a <= 16, and mainly the v(t) = 0 and 1 torsional states. The Hamiltonian model describes our data well. The model was applied to derive a line list for radio-astronomical observations. We report a tentative detection of (CH3OH)-O-17 along with secure detections of the more abundant isotopologs of methanol toward Sgr B2(N2b). The derived column densities yield isotopic ratios C-12/C-13 = 25, O-16/O-18 = 240, and O-18/O-17 = 3.3, which are consistent with values found earlier for other molecules in Sgr B2. Conclusions. The agreement between the O-18/O-17 isotopic ratio that we obtained for methanol and the O-18/O-17 ratios reported in the past for other molecules in Sgr B2(N) strongly supports our tentative interstellar identification of (CH3OH)-O-17. The accuracy of the derived line list is sufficient for further radio astronomical searches for this methanol isotopolog toward other star-forming regions.

We want to investigate the influence of the powerful outflow driven by the hot core Sgr B2(N1) on the gas molecular inventory of the surrounding medium. We used the data taken as part of the 3 mm imaging spectral-line survey ReMoCA (Re-exploring Molecular Complexity with ALMA). Integrated intensity maps of SO and SiO emission reveal a bipolar structure with blue-shifted emission dominantly extending to the SE from the centre of the hot core and red-shifted emission to the NW. This is also prominently observed in emission of other S-bearing molecules and species that only contain N as a heavy element, including COMs, but also CH3OH, CH3CHO, HNCO, and NH2CHO. For a selection of COMs and simpler species, spectra were modelled under the assumption of LTE and population diagrams were derived at two positions, one in each outflow lobe. From this analysis, we obtained rotational temperatures, which are in a range of ~100-200K, and column densities. Abundances were subsequently compared to predictions of astrochemical models and to observations of L1157-B1, a position located in the well-studied outflow of the low-mass protostar L1157, and the source G+0.693-0.027, located in the Sgr B2 molecular cloud complex. Given the short distance of the analysed outflow positions to the centre of Sgr B2(N1), we propose a scenario in which a phase of hot-core chemistry (i.e. thermal desorption of ice species and high-temperature gas-phase chemistry) preceded a shock wave. The subsequent compression and further heating of the material resulted in the accelerated destruction of (mainly O-bearing) molecules. Gas-phase formation of cyanides seems to be able to compete with their destruction in the post-shock gas. Abundances of HCnN (n=3,5) are enhanced in the outflow component pointing to (additional) gas-phase formation. To confirm such a scenario, appropriate chemical shock models need to be run.

(abridged) We have mapped the prestellar core H-MM1 in Ophiuchus in rotational lines of ortho-H2D+ (oH2D+), N2H+, and DCO+ at the wavelength 0.8 mm with the Large APEX sub-Millimeter Array (LAsMA) multibeam receiver of the Atacama Pathfinder EXperiment (APEX) telescope. We also ran a series of chemistry models to predict the abundance distributions of the observed molecules, and to estimate the effect of the cosmic-ray ionisation rate on their abundances. The three line maps show different distributions. The oH2D+ map is extended and outlines the general structure of the core, while N2H+ mainly shows the density maxima, and the DCO+ emission peaks are shifted towards one edge of the core where a region of enhanced desorption has been found previously. According to the chemical simulation, the fractional oH2D+ abundance remains relatively high in the centre of the core, and its column density correlates strongly with the cosmic-ray ionisation rate. Simulated line maps constrain the cosmic-ray ionisation rate per hydrogen molecule to be low, between 5e-18/s and 1e-17/s in the H-MM1 core. This estimate agrees with the gas temperature measured in the core. Modelling line emission of oH2D+ provides a straightforward method of determining the cosmic-ray ionisation rate in dense clouds, where the primary ion, H3+, is not observable.