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109 results on '"Sims, I. R."'

1. Mass ejection and time variability in protostellar outflows: Cep E. SOLIS XVI

Author

Schutzer, A. de A., Rivera-Ortiz, P. R., Lefloch, B., Gusdorf, A., Favre, C., Segura-Cox, D., Lopez-Sepulcre, A., Neri, R., Ospina-Zamudio, J., De Simone, M., Codella, C., Viti, S., Podio, L., Pineda, J., O'Donoghue, R., Ceccarelli, C., Caselli, P., Alves, F., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Bottinelli, S., Caux, E., Chacón-Tanarro, A., Dulieu, F., Enrique-Romero, J., Fontani, F., Feng, S., Holdship, J., Jiménez-Serra, I., Al-Edhari, A. Jaber, Kahane, C., Lattanzi, V., Oya, Y., Punanova, A., Rimola, A., Sakai, N., Spezzano, S., Sims, I. R., Taquet, V., Testi, L., Theulé, P., Ugliengo, P., Vastel, C., Vasyunin, A. I., Vazart, F., Yamamoto, S., and Witzel, A.

Subjects
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Astrophysics of Galaxies
Abstract

Protostellar jets are an important agent of star formation feedback, tightly connected with the mass-accretion process. The history of jet formation and mass-ejection provides constraints on the mass accretion history and the nature of the driving source. We want to characterize the time-variability of the mass-ejection phenomena at work in the Class 0 protostellar phase, in order to better understand the dynamics of the outflowing gas and bring more constraints on the origin of the jet chemical composition and the mass-accretion history. We have observed the emission of the CO 2-1 and SO N_J=5_4-4_3 rotational transitions with NOEMA, towards the intermediate-mass Class 0 protostellar system Cep E. The CO high-velocity jet emission reveals a central component associated with high-velocity molecular knots, also detected in SO, surrounded by a collimated layer of entrained gas. The gas layer appears to accelerate along the main axis over a length scale delta_0 ~700 au, while its diameter gradually increases up to several 1000au at 2000au from the protostar. The jet is fragmented into 18 knots of mass ~10^-3 Msun, unevenly distributed between the northern and southern lobes, with velocity variations up to 15 km/s close to the protostar, well below the jet terminal velocities. The knot interval distribution is approximately bimodal with a scale of ~50-80yr close to the protostar and ~150-200yr at larger distances >12". The mass-loss rates derived from knot masses are overall steady, with values of 2.7x10^-5 Msun/yr (8.9x10^-6 Msun/yr) in the northern (southern) lobe. The interaction of the ambient protostellar material with high-velocity knots drives the formation of a molecular layer around the jet, which accounts for the higher mass-loss rate in the north. The jet dynamics are well accounted for by a simple precession model with a period of 2000yr and a mass-ejection period of 55yr., Comment: 13 pages, 9 figures, 3 table. Accepted in A&A

Published
2022
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2. Absolute measurements of state-to-state rotational energy transfer between CO and H2 at interstellar temperatures

Author

Labiad, H., Fournier, M., Mertens, L. A., Faure, A., Carty, D., Stoecklin, T., Jankowski, P., Szalewicz, K., Picard, S. D. Le, and Sims, I. R.

Subjects
Physics - Chemical Physics
Abstract

Experimental measurements and theoretical calculations of state-to-state rate coefficients for rotational energy transfer of CO in collision with H$_2$ are reported at the very low temperatures prevailing in dense interstellar clouds (5 - 20 K). Detailed agreement between quantum state-selected experiments performed in cold supersonic flows using time-resolved infrared - vacuum-ultraviolet double resonance spectroscopy and close-coupling quantum scattering calculations confirms the validity of the calculations for collisions between the two most abundant molecules in the interstellar medium., Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev. A. Letter (21/12/2021)

Published
2022
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3. Seeds of Life in Space (SOLIS).VII. Discovery of a cold dense methanol blob toward the L1521F VeLLO system

Author

Favre, C., Vastel, C., Jimenez-Serra, I., Quénard, D., Caselli, P., Ceccarelli, C., Chacón-Tanarro, A., Fontani, F., Holdship, J., Oya, Y., Punanova, A., Sakai, N., Spezzano, S., Yamamoto, S., Neri, R., López-Sepulcre, A., Alves, F., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Codella, C., Caux, E., De Simone, M., Romero, J. Enrique, Dulieu, F., Feng, S., Al-Edhari, A. Jaber, Lefloch, B., Ospina-Zamudio, J., Pineda, J., Podio, L., Rimola, A., Segura-Cox, D., Sims, I. R., Taquet, V., Testi, L., Theulé, P., Ugliengo, P., Vasyunin, A. I., Vazart, F., Viti, S., and Witzel, A.

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

The SOLIS (Seeds Of Life In Space) IRAM/NOEMA Large Program aims at studying a set of crucial complex organic molecules in a sample of sources, with well-known physical structure, covering the various phases of Solar-type star formation. One representative object of the transition from the prestellar core to the protostar phases has been observed toward the Very Low Luminosity Object (VeLLO) called L1521F. This type of source is important to study to make the link between prestellar cores and Class 0 sources and also to constrain the chemical evolution during the process of star formation. Two frequency windows (81.6-82.6 GHz and 96.65-97.65 GHz) were used to observe the emission from several complex organics toward the L1521F VeLLO. Only 2 transitions of methanol (A+, E2) have been detected in the narrow window centered at 96.7 GHz (with an upper limit on E1) in a very compact emission blob (~7'' corresponding to ~1000au) toward the NE of the L1521F protostar. The CS 2-1 transition is also detected within the WideX bandwidth. Consistently, with what has been found in prestellar cores, the methanol emission appears ~1000au away from the dust peak. The location of the methanol blob coincides with one of the filaments previously reported in the literature. The Tex of the gas inferred from methanol is (10$\pm$2) K, while the H2 gas density (estimated from the detected CS 2-1 emission and previous CS 5-4 ALMA obs.) is a factor >25 higher than the density in the surrounding environment (n(H2) >10$^{7}$ cm$^{-3}$). From its compactness, low excitation temperature and high gas density, we suggest that the methanol emission detected with NOEMA is either a cold and dense shock-induced blob, recently formed ($\leq$ few hundred years) by infalling gas or a cold and dense fragment that may have just been formed as a result of the intense gas dynamics found within the L1521F VeLLO system., Comment: 11 pages, 7 figures, 3 tables, accepted for publication by A&A

Published
2020
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4. SOLIS IV. Hydrocarbons in the OMC-2 FIR 4 region, a probe of energetic particle irradiation of the region

Author

Favre, C., Ceccarelli, C., López-Sepulcre, A., Fontani, F., Neri, R., Manigand, S., Kama, M., Caselli, P., Al-Edhari, A. Jaber, Kahane, C., Alves, F., Balucani, N., Bianchi, E., Caux, E., Codella, C., Dulieu, F., Pineda, J. E., Sims, I. R., and Theulé, P.

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

We report new interferometric images of cyclopropenylidene, c-C$_3$H$_2$, towards the young protocluster OMC-2 FIR\,4. The observations were performed at 82 and 85 GHz with the NOrthern Extended Millimeter Array (NOEMA) as part of the project Seeds Of Life In Space (SOLIS). In addition, IRAM-30m data observations were used to investigate the physical structure of OMC-2 FIR\,4. We find that the c-C$_3$H$_2$ gas emits from the same region where previous SOLIS observations showed bright HC$_5$N emission. From a non-LTE analysis of the IRAM-30m data, the c-C$_3$H$_2$ gas has an average temperature of $\sim$40K, a H$_2$ density of $\sim$3$\times$10$^{5}$~cm$^{-3}$, and a c-C$_3$H$_2$ abundance relative to H$_2$ of ($7\pm1$)$\times$10$^{-12}$. In addition, the NOEMA observations provide no sign of significant c-C$_3$H$_2$ excitation temperature gradients across the region (about 3-4 beams), with T$_{ex}$ in the range 8$\pm$3 up to 16$\pm$7K. We thus infer that our observations are inconsistent with a physical interaction of the OMC-2 FIR\,4 envelope with the outflow arising from OMC-2 FIR\,3, as claimed by previous studies. The comparison of the measured c-C$_3$H$_2$ abundance with the predictions from an astrochemical PDR model indicates that OMC-2 FIR\,4 is irradiated by a FUV field $\sim$1000 times larger than the interstellar one, and by a flux of ionising particles $\sim$4000 times larger than the canonical value of $1\times10^{-17}$~s$^{-1}$ from the Galaxy cosmic rays, which is consistent with our previous HC$_5$N observations. This provides an important and independent confirmation of other studies that one or more sources inside the OMC-2 FIR\,4 region emit energetic ($\geq10$~MeV) particles., Comment: Accepted for publication in ApJ - 14 pages, 10 figures, 4 tables

Published
2018
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5. SOLIS II. Carbon-chain growth in the Solar-type protocluster OMC2-FIR4

Author

Fontani, F., Ceccarelli, C., Favre, C., Caselli, P., Neri, R., Sims, I. R., Kahane, C., Alves, F., Balucani, N., Bianchi, E., Caux, E., Al-Edhari, A. Jaber, Lopez-Sepulcre, A., Pineda, J. E., Bachiller, R., Bizzocchi, L., Bottinelli, S., Chacon-Tanarro, A., Choudhury, R., Codella, C., Coutens, A., Dulieu, F., Feng, S., Rimola, A., Hily-Blant, P., Holdship, J., Jimenez-Serra, I., Laas, J., Lefloch, B., Oya, Y., Podio, L., Pon, A., Punanova, A., Quenard, D., Sakai, N., Spezzano, S., Taquet, V., Testi, L., Theulé, P., Ugliengo, P., Vastel, C., Vasyunin, A. I., Viti, S., Yamamoto, S., and Wiesenfeld, L.

Subjects
Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics
Abstract

The interstellar delivery of carbon atoms locked into molecules might be one of the key ingredients for the emergence of life. Cyanopolyynes are carbon chains delimited at their two extremities by an atom of hydrogen and a cyano group, so that they might be excellent reservoirs of carbon. The simplest member, HC3N, is ubiquitous in the galactic interstellar medium and found also in external galaxies. Thus, understanding the growth of cyanopolyynes in regions forming stars similar to our Sun, and what affects it, is particularly relevant. In the framework of the IRAM/NOEMA Large Program SOLIS (Seeds Of Life In Space), we have obtained a map of two cyanopolyynes, HC3N and HC5N, in the protocluster OMC2-FIR4. Because our Sun is thought to be born in a rich cluster, OMC2-FIR4 is one of the closest and best known representatives of the environment in which the Sun may have been born. We find a HC3N/HC5N abundance ratio across the source in the range ~ 1 - 30, with the smallest values (< 10) in FIR5 and in the Eastern region of FIR4. The ratios < 10 can be reproduced by chemical models only if: (1) the cosmic-ray ionisation rate $\zeta$ is ~ $4 \times 10^{-14}$ s$^{-1}$; (2) the gaseous elemental ratio C/O is close to unity; (3) O and C are largely depleted. The large $\zeta$ is comparable to that measured in FIR4 by previous works and was interpreted as due to a flux of energetic (> 10 MeV) particles from embedded sources. We suggest that these sources could lie East of FIR4 and FIR5. A temperature gradient across FIR4, with T decreasing by about 10 K, could also explain the observed change in the HC3N/HC5N line ratio, without the need of a cosmic ray ionisation rate gradient. However, even in this case, a high constant cosmic-ray ionisation rate (of the order of $10^{-14}$ s$^{-1}$) is necessary to reproduce the observations., Comment: 12 pages, 8 figures, accepted for publication in A&A

Published
2017
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6. The 2014 KIDA network for interstellar chemistry

Author

Wakelam, V., Loison, J. -C., Herbst, E., Pavone, B., Bergeat, A., Béroff, K., Chabot, M., Faure, A., Galli, D., Geppert, W. D., Gerlich, D., Gratier, P., Harada, N., Hickson, K. M., Honvault, P., Klippenstein, S. J., Picard, S. D. Le, Nyman, G., Ruaud, M., Schlemmer, S., Sims, I. R., Talbi, D., Tennyson, J., and Wester, R.

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011., Comment: Accepted for publication in ApJS on February 26th, 2015

Published
2015
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7. A KInetic Database for Astrochemistry (KIDA)

Author

Wakelam, V., Herbst, E., Loison, J. -C., Smith, I. W. M., Chandrasekaran, V., Pavone, B., Adams, N. G., Bacchus-Montabonel, M. -C., Bergeat, A., Béroff, K., Bierbaum, V. M., Chabot, M., Dalgarno, A., van Dishoeck, E. F., Faure, A., Geppert, W. D., Gerlich, D., Galli, D., Hébrard, E., Hersant, F., Hickson, K. M., Honvault, P., Klippenstein, S. J., Picard, S. Le, Nyman, G., Pernot, P., Schlemmer, S., Selsis, F., Sims, I. R., Talbi, D., Tennyson, J., Troe, J., Wester, R., and Wiesenfeld, L.

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

We present a novel chemical database for gas-phase astrochemistry. Named the KInetic Database for Astrochemistry (KIDA), this database consists of gas-phase reactions with rate coefficients and uncertainties that will be vetted to the greatest extent possible. Submissions of measured and calculated rate coefficients are welcome, and will be studied by experts before inclusion into the database. Besides providing kinetic information for the interstellar medium, KIDA is planned to contain such data for planetary atmospheres and for circumstellar envelopes. Each year, a subset of the reactions in the database (kida.uva) will be provided as a network for the simulation of the chemistry of dense interstellar clouds with temperatures between 10 K and 300 K. We also provide a code, named Nahoon, to study the time-dependent gas-phase chemistry of 0D and 1D interstellar sources., Comment: Accepted for publication in ApJS

Published
2012
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10. SOLIS

Author

de A. Schutzer, A., primary, Rivera-Ortiz, P. R., additional, Lefloch, B., additional, Gusdorf, A., additional, Favre, C., additional, Segura-Cox, D., additional, López-Sepulcre, A., additional, Neri, R., additional, Ospina-Zamudio, J., additional, De Simone, M., additional, Codella, C., additional, Viti, S., additional, Podio, L., additional, Pineda, J., additional, O’Donoghue, R., additional, Ceccarelli, C., additional, Caselli, P., additional, Alves, F., additional, Bachiller, R., additional, Balucani, N., additional, Bianchi, E., additional, Bizzocchi, L., additional, Bottinelli, S., additional, Caux, E., additional, Chacón-Tanarro, A., additional, Dulieu, F., additional, Enrique-Romero, J., additional, Fontani, F., additional, Feng, S., additional, Holdship, J., additional, Jiménez-Serra, I., additional, Jaber Al-Edhari, A., additional, Kahane, C., additional, Lattanzi, V., additional, Oya, Y., additional, Punanova, A., additional, Rimola, A., additional, Sakai, N., additional, Spezzano, S., additional, Sims, I. R., additional, Taquet, V., additional, Testi, L., additional, Theulé, P., additional, Ugliengo, P., additional, Vastel, C., additional, Vasyunin, A. I., additional, Vazart, F., additional, Yamamoto, S., additional, and Witzel, A., additional

Published
2022
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12. A new instrument for kinetics and branching ratio studies of gas phase collisional processes at very low temperatures

Author

Durif, O., primary, Capron, M., additional, Messinger, J. P., additional, Benidar, A., additional, Biennier, L., additional, Bourgalais, J., additional, Canosa, A., additional, Courbe, J., additional, Garcia, G. A., additional, Gil, J. F., additional, Nahon, L., additional, Okumura, M., additional, Rutkowski, L., additional, Sims, I. R., additional, Thiévin, J., additional, and Le Picard, S. D., additional

Published
2021
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13. Seeds of Life in Space (SOLIS)

Author

Taquet, V., primary, Codella, C., additional, De Simone, M., additional, López-Sepulcre, A., additional, Pineda, J. E., additional, Segura-Cox, D., additional, Ceccarelli, C., additional, Caselli, P., additional, Gusdorf, A., additional, Persson, M. V., additional, Alves, F., additional, Caux, E., additional, Favre, C., additional, Fontani, F., additional, Neri, R., additional, Oya, Y., additional, Sakai, N., additional, Vastel, C., additional, Yamamoto, S., additional, Bachiller, R., additional, Balucani, N., additional, Bianchi, E., additional, Bizzocchi, L., additional, Chacón-Tanarro, A., additional, Dulieu, F., additional, Enrique-Romero, J., additional, Feng, S., additional, Holdship, J., additional, Lefloch, B., additional, Jaber Al-Edhari, A., additional, Jiménez-Serra, I., additional, Kahane, C., additional, Lattanzi, V., additional, Ospina-Zamudio, J., additional, Podio, L., additional, Punanova, A., additional, Rimola, A., additional, Sims, I. R., additional, Spezzano, S., additional, Testi, L., additional, Theulé, P., additional, Ugliengo, P., additional, Vasyunin, A. I., additional, Vazart, F., additional, Viti, S., additional, and Witzel, A., additional

Published
2020
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14. Seeds of Life in Space (SOLIS)

Author

Favre, C., primary, Vastel, C., additional, Jimenez-Serra, I., additional, Quénard, D., additional, Caselli, P., additional, Ceccarelli, C., additional, Chacón-Tanarro, A., additional, Fontani, F., additional, Holdship, J., additional, Oya, Y., additional, Punanova, A., additional, Sakai, N., additional, Spezzano, S., additional, Yamamoto, S., additional, Neri, R., additional, López-Sepulcre, A., additional, Alves, F., additional, Bachiller, R., additional, Balucani, N., additional, Bianchi, E., additional, Bizzocchi, L., additional, Codella, C., additional, Caux, E., additional, De Simone, M., additional, Enrique Romero, J., additional, Dulieu, F., additional, Feng, S., additional, Jaber Al-Edhari, A., additional, Lefloch, B., additional, Ospina-Zamudio, J., additional, Pineda, J., additional, Podio, L., additional, Rimola, A., additional, Segura-Cox, D., additional, Sims, I. R., additional, Taquet, V., additional, Testi, L., additional, Theulé, P., additional, Ugliengo, P., additional, Vasyunin, A. I., additional, Vazart, F., additional, Viti, S., additional, and Witzel, A., additional

Published
2020
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15. Seeds of Life in Space (SOLIS)

Author

Favre, C., Vastel, C., Jimenez-Serra, I., Quénard, D., Caselli, P., Ceccarelli, C., Chacón-Tanarro, A., Fontani, F., Holdship, J., Oya, Y., Punanova, A., Sakai, N., Spezzano, S., Yamamoto, S., Neri, R., López-Sepulcre, A., Alves, F., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Codella, C., Caux, E., De Simone, M., Enrique Romero, J., Dulieu, F., Feng, S., Jaber Al-Edhari, A., Lefloch, B., Ospina-Zamudio, J., Pineda, J., Podio, L., Rimola, A., Segura-Cox, D., Sims, I. R., Taquet, V., Testi, L., Theulé, P., Ugliengo, P., Vasyunin, A. I., Vazart, F., Viti, S., and Witzel, A.

Subjects
Astrochemistry
Published
2020

16. Seeds of Life in Space (SOLIS): VI. Chemical evolution of sulfuretted species along the outflows driven by the low-mass protostellar binary NGC 1333-IRAS4A

Author

Taquet, V., Codella, C., De Simone, M., López-Sepulcre, A., Pineda, J. E., Segura-Cox, D., Ceccarelli, C., Caselli, P., Gusdorf, A., Persson, M. V., Alves, F., Caux, E., Favre, C., Fontani, F., Neri, R., Oya, Y., Sakai, N., Vastel, C., Yamamoto, S., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Chacón-Tanarro, A., Dulieu, F., Enrique-Romero, J., Feng, S., Holdship, J., Lefloch, B., Jaber, Al-Edhari, A., Jiménez-Serra, I., Kahane, C., Lattanzi, V., Ospina-Zamudio, J., Podio, L., Punanova, A., Rimola, A., Sims, I. R., Spezzano, S., Testi, L., Theulé, P., Ugliengo, P., Vasyunin, A. I., Vazart, F., Viti, S., Witzel, A., Taquet, V., Codella, C., De Simone, M., López-Sepulcre, A., Pineda, J. E., Segura-Cox, D., Ceccarelli, C., Caselli, P., Gusdorf, A., Persson, M. V., Alves, F., Caux, E., Favre, C., Fontani, F., Neri, R., Oya, Y., Sakai, N., Vastel, C., Yamamoto, S., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Chacón-Tanarro, A., Dulieu, F., Enrique-Romero, J., Feng, S., Holdship, J., Lefloch, B., Jaber, Al-Edhari, A., Jiménez-Serra, I., Kahane, C., Lattanzi, V., Ospina-Zamudio, J., Podio, L., Punanova, A., Rimola, A., Sims, I. R., Spezzano, S., Testi, L., Theulé, P., Ugliengo, P., Vasyunin, A. I., Vazart, F., Viti, S., and Witzel, A.

Abstract

Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC 1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC 1333-IRAS4A in the 1.3, 2, and 3 mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east-south west direction. SO is detected at extremely high radial velocity up to + 25 km s-1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm-3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputter

Published
2020

17. Seeds of Life in Space (SOLIS): VII. Discovery of a cold dense methanol blob toward the L1521F VeLLO system

Author

Favre, C., Vastel, C., Jimenez-Serra, I., Quénard, D., Caselli, P., Ceccarelli, C., Chacón-Tanarro, A., Fontani, F., Holdship, J., Oya, Y., Punanova, A., Sakai, N., Spezzano, S., Yamamoto, S., Neri, R., López-Sepulcre, A., Alves, F., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Codella, C., Caux, E., De, Simone, M., Enrique, Romero, J., Dulieu, F., Feng, S., Jaber, Al-Edhari, A., Lefloch, B., Ospina-Zamudio, J., Pineda, J., Podio, L., Rimola, A., Segura-Cox, D., Sims, I. R., Taquet, V., Testi, L., Theulé, P., Ugliengo, P., Vasyunin, A. I., Vazart, F., Viti, S., Witzel, A., Favre, C., Vastel, C., Jimenez-Serra, I., Quénard, D., Caselli, P., Ceccarelli, C., Chacón-Tanarro, A., Fontani, F., Holdship, J., Oya, Y., Punanova, A., Sakai, N., Spezzano, S., Yamamoto, S., Neri, R., López-Sepulcre, A., Alves, F., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Codella, C., Caux, E., De, Simone, M., Enrique, Romero, J., Dulieu, F., Feng, S., Jaber, Al-Edhari, A., Lefloch, B., Ospina-Zamudio, J., Pineda, J., Podio, L., Rimola, A., Segura-Cox, D., Sims, I. R., Taquet, V., Testi, L., Theulé, P., Ugliengo, P., Vasyunin, A. I., Vazart, F., Viti, S., and Witzel, A.

Abstract

Aims. The Seeds Of Life In Space IRAM/NOEMA large program aims at studying a set of crucial complex organic molecules in a sample of sources with a well-known physical structure that covers the various phases of solar-type star formation. One representative object of the transition from the prestellar core to the protostar phases has been observed toward the very low luminosity object (VeLLO) L1521F. This type of source is important to study to link prestellar cores and Class 0 sources and also to constrain the chemical evolution during the process of star formation. Methods. Two frequency windows (81.6-82.6 GHz and 96.65-97.65 GHz) were used to observe the emission from several complex organics toward the L1521F VeLLO. These setups cover transitions of ketene (H2CCO), propyne (CH3CCH), formamide (NH2CHO), methoxy (CH3O), methanol (CH3OH), dimethyl ether (CH3OCH3), and methyl formate (HCOOCH3). Results. Only two transitions of methanol (A+, E2) have been detected in the narrow window centered at 96.7 GHz (with an upper limit on E1) in a very compact emission blob (∼7″ corresponding to ∼1000 au) toward the northeast of the L1521F protostar. The CS 2-1 transition is also detected within theWideX bandwidth. Consistently with what has been found in prestellar cores, the methanol emission appears ∼1000 au away from the dust peak. The location of the methanol blob coincides with one of the filaments that have previously been reported in the literature. The excitation temperature of the gas inferred from methanol is (10 ± 2) K, while the H2 gas density (estimated from the detected CS 2-1 emission and previous CS 5-4 ALMA observations) is a factor >25 higher than the density in the surrounding environment (n(H2) ≥ 107 cm-3). Conclusions. Based on its compactness, low excitation temperature, and high gas density, we suggest that the methanol emission detected with NOEMA is (i) either a cold and dense shock-induced blob that formed recently (≤ a few hundred years) by infal

Published
2020

20. SOLIS IV. Hydrocarbons in the OMC-2 FIR4 Region, a Probe of Energetic Particle Irradiation of the Region

Author

Favre, C., primary, Ceccarelli, C., additional, López-Sepulcre, A., additional, Fontani, F., additional, Neri, R., additional, Manigand, S., additional, Kama, M., additional, Caselli, P., additional, Al-Edhari, A. Jaber, additional, Kahane, C., additional, Alves, F., additional, Balucani, N., additional, Bianchi, E., additional, Caux, E., additional, Codella, C., additional, Dulieu, F., additional, Pineda, J. E., additional, Sims, I. R., additional, and Theulé, P., additional

Published
2018
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21. Experimental and theoretical study of intramultiplet transitions in collisions of C([sup 3]P) and Si([sup 3]P) with He.

Author

Le Picard, S. D., Honvault, P., Bussery-Honvault, B., Canosa, A., Laubé, S., Launay, J.-M., Rowe, Bertrand, Chastaing, D., and Sims, I. R.

Subjects
PHOSPHIDES, COLLISIONS (Nuclear physics)
Abstract

We present a combined theoretical and experimental study of intramultiplet transitions in collisions of C([SUP3]P) and Si([SUP3]P) with He. Relaxation rate constants have been measured using the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) technique at 15 K for C([SUP3]P) + He and over the 15-49 K temperature range for Si([SUP3]P) + He. Three sets of interaction potentials have been generated for the [SUP3]Σ[SUP-] and [SUP3]∏ electronic states of CHe and SiHe systems. Quantum-mechanical calculations have been performed on these potential curves for the spin-orbit relaxation and excitation. Cross sections and rate constants are very sensitive to the interaction potential. For the Si([SUP3]P) + He system, an overall good agreement between the theoretical and experimental rate constants is found with the best quality interaction potential, while for the C([SUP3]P) + He system experimental rate constants are much smaller than the theoretical ones. [ABSTRACT FROM AUTHOR]

Published
2002
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22. SOLIS IV. Hydrocarbons in the OMC-2 FIR4 Region, a Probe of Energetic Particle Irradiation of the Region

Author

Favre, C., Ceccarelli, C., Lopez-Sepulcre, A., Fontani, F., Neri, R., Manigand, Sébastian, Kama, M., Caselli, P., Al-Edhari, A. Jaber, Kahane, C., Alves, F., Balucani, N., Bianchi, E., Caux, E., Codella, C., Dulieu, F., Pineda, J. E., Sims, I. R., Theule, P., Favre, C., Ceccarelli, C., Lopez-Sepulcre, A., Fontani, F., Neri, R., Manigand, Sébastian, Kama, M., Caselli, P., Al-Edhari, A. Jaber, Kahane, C., Alves, F., Balucani, N., Bianchi, E., Caux, E., Codella, C., Dulieu, F., Pineda, J. E., Sims, I. R., and Theule, P.

Published
2018

23. Seeds Of Life In Space (SOLIS): The Organic Composition Diversity at 300–1000 au Scale in Solar-type Star-forming Regions

Author

Ceccarelli, C., primary, Caselli, P., additional, Fontani, F., additional, Neri, R., additional, López-Sepulcre, A., additional, Codella, C., additional, Feng, S., additional, Jiménez-Serra, I., additional, Lefloch, B., additional, Pineda, J. E., additional, Vastel, C., additional, Alves, F., additional, Bachiller, R., additional, Balucani, N., additional, Bianchi, E., additional, Bizzocchi, L., additional, Bottinelli, S., additional, Caux, E., additional, Chacón-Tanarro, A., additional, Choudhury, R., additional, Coutens, A., additional, Dulieu, F., additional, Favre, C., additional, Hily-Blant, P., additional, Holdship, J., additional, Kahane, C., additional, Al-Edhari, A. Jaber, additional, Laas, J., additional, Ospina, J., additional, Oya, Y., additional, Podio, L., additional, Pon, A., additional, Punanova, A., additional, Quenard, D., additional, Rimola, A., additional, Sakai, N., additional, Sims, I. R., additional, Spezzano, S., additional, Taquet, V., additional, Testi, L., additional, Theulé, P., additional, Ugliengo, P., additional, Vasyunin, A. I., additional, Viti, S., additional, Wiesenfeld, L., additional, and Yamamoto, S., additional

Published
2017
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24. Seeds of Life in Space (SOLIS)

Author

Fontani, F., primary, Ceccarelli, C., additional, Favre, C., additional, Caselli, P., additional, Neri, R., additional, Sims, I. R., additional, Kahane, C., additional, Alves, F. O., additional, Balucani, N., additional, Bianchi, E., additional, Caux, E., additional, Jaber Al-Edhari, A., additional, Lopez-Sepulcre, A., additional, Pineda, J. E., additional, Bachiller, R., additional, Bizzocchi, L., additional, Bottinelli, S., additional, Chacon-Tanarro, A., additional, Choudhury, R., additional, Codella, C., additional, Coutens, A., additional, Dulieu, F., additional, Feng, S., additional, Rimola, A., additional, Hily-Blant, P., additional, Holdship, J., additional, Jimenez-Serra, I., additional, Laas, J., additional, Lefloch, B., additional, Oya, Y., additional, Podio, L., additional, Pon, A., additional, Punanova, A., additional, Quenard, D., additional, Sakai, N., additional, Spezzano, S., additional, Taquet, V., additional, Testi, L., additional, Theulé, P., additional, Ugliengo, P., additional, Vastel, C., additional, Vasyunin, A. I., additional, Viti, S., additional, Yamamoto, S., additional, and Wiesenfeld, L., additional

Published
2017
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25. Ultra-low temperature kinetics of neutral–neutral reactions: New experimental and theoretical results for OH+HBr between 295 and 23 K.

Author

Sims, I. R., Smith, I. W. M., Clary, D. C., Bocherel, P., and Rowe, B. R.

Subjects
*RADICALS (Chemistry), *CHEMICAL reactions, *QUANTUM theory
Abstract

The first determination of the rate of reaction of OH radicals with HBr at temperatures below 249 K is reported. Rate constants measured from 295 to 23 K increase monotonically with decrease in temperature and are faster than has previously been thought at the temperatures present in the mid and low stratosphere. The observed negative temperature dependence is well predicted by a simple formula deduced from quantum scattering calculations employing the rotating bond approximation. [ABSTRACT FROM AUTHOR]

Published
1994
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26. Ultralow temperature kinetics of neutral–neutral reactions. The technique and results for the reactions CN+O2 down to 13 K and CN+NH3 down to 25 K.

Author

Sims, I. R., Queffelec, J.-L., Defrance, A., Rebrion-Rowe, C., Travers, D., Bocherel, P., Rowe, B. R., and Smith, I. W. M.

Subjects
*DYNAMICS, *CHEMICAL reactions, *PHOTOCHEMISTRY
Abstract

An entirely new experimental method is described which enables the rate constants of neutral–neutral gas-phase reactions to be measured at ultralow temperatures. The measurements are made by applying the pulsed laser photolysis (PLP), laser-induced fluorescence (LIF) technique of studying the kinetics of free radical reactions in the ultracold environment provided by the gas flow in a Cinétique de Réaction en Ecoulement Supersonique Uniforme (CRESU) apparatus. The experimental method is described in some detail and its application and limitations are discussed. Results are reported for the reactions of CN radicals with O2 and NH3. For reaction (1) between CN and O2 data are reported for the temperature range T=13–295 K and the rate constants are well-matched by the expression k1(T)=(2.49±0.17)×10-11 (T/298)(-0.63±0.04) cm3 molecule-1 s-1. For reaction (2) between CN and NH3, rate constants in the temperature range T=25–295 K fit the expression k2(T)=(2.77±0.67)×10-11 (T/298)(-1.14±0.15) cm3 molecule-1 s-1. The kinetic data are discussed in terms of the latest quantum chemical and reaction rate theories for these systems. [ABSTRACT FROM AUTHOR]

Published
1994
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27. Femtosecond real-time probing of reactions. VIII. The bimolecular reaction Br+I2.

Author

Sims, I. R., Gruebele, M., Potter, E. D., and Zewail, A. H.

Subjects
*BIMOLECULAR collisions, *CHEMICAL reactions
Abstract

In this paper, we discuss the experimental technique for real-time measurement of the lifetimes of the collision complex of bimolecular reactions. An application to the atom–molecule Br+I2 reaction at two collision energies is made. Building on our earlier Communication [J. Chem. Phys. 95, 7763 (1991)], we report on the observed transients and lifetimes for the collision complex, the nature of the transition state, and the dynamics near threshold. Classical trajectory calculations provide a framework for deriving the global nature of the reactive potential energy surface, and for discussing the real-time, scattering, and asymptotic (product-state distribution) aspects of the dynamics. These experimental and theoretical results are compared with the extensive array of kinetic, crossed beam, and theoretical studies found in the literature for halogen radical–halogen molecule exchange reactions. [ABSTRACT FROM AUTHOR]

Published
1992
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28. Femtosecond probing of bimolecular reactions: The collision complex.

Author

Gruebele, M., Sims, I. R., Potter, E. D., and Zewail, A. H.

Subjects
*COLLISIONS (Physics), *MOLECULAR dynamics, *POTENTIAL energy surfaces
Abstract

Details a proposed approach to directly probe the femtosecond dynamics of the collision complex of a bimolecular reaction on the ground state potential energy surface. Characteristics of the atom-exchange reaction; Apparatus for the femtosecond molecular beam arrangement.

Published
1991
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29. Seeds Of Life In Space (SOLIS): The Organic Composition Diversity at 300-1000 au Scale in Solar-type Star-forming Regions

Author

Ceccarelli, C., Caselli, P., Fontani, F., Neri, R., Lopez-Sepulcre, A., Codella, C., Feng, S., Jimenez-Serra, I., Lefloch, B., Pineda, J. E., Vastel, C., Alves, F., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Bottinelli, S., Caux, E., Chacon-Tanarro, A., Choudhury, R., Coutens, A., Dulieu, F., Favre, C., Hily-Blant, P., Holdship, J., Kahane, C., Al-Edhari, A. Jaber, Laas, J., Ospina, J., Oya, Y., Podio, L., Pon, A., Punanova, A., Quenard, D., Rimola, A., Sakai, N., Sims, I. R., Spezzano, S., Taquet, V., Testi, L., Theule, P., Ugliengo, P., Vasyunin, A. I., Viti, S., Wiesenfeld, L., Yamamoto, S., Ceccarelli, C., Caselli, P., Fontani, F., Neri, R., Lopez-Sepulcre, A., Codella, C., Feng, S., Jimenez-Serra, I., Lefloch, B., Pineda, J. E., Vastel, C., Alves, F., Bachiller, R., Balucani, N., Bianchi, E., Bizzocchi, L., Bottinelli, S., Caux, E., Chacon-Tanarro, A., Choudhury, R., Coutens, A., Dulieu, F., Favre, C., Hily-Blant, P., Holdship, J., Kahane, C., Al-Edhari, A. Jaber, Laas, J., Ospina, J., Oya, Y., Podio, L., Pon, A., Punanova, A., Quenard, D., Rimola, A., Sakai, N., Sims, I. R., Spezzano, S., Taquet, V., Testi, L., Theule, P., Ugliengo, P., Vasyunin, A. I., Viti, S., Wiesenfeld, L., and Yamamoto, S.

Published
2017

30. Seeds of Life in Space (SOLIS): I. Carbon-chain growth in the Solar-type protocluster OMC2-FIR4

Author

Fontani, F., Ceccarelli, C., Favre, C., Caselli, P., Neri, R., Sims, I. R., Kahane, C., Alves, F. O., Balucani, N., Bianchi, E., Caux, E., Jaber, Al-Edhari, A., Lopez-Sepulcre, A., Pineda, J. E., Bachiller, R., Bizzocchi, L., Bottinelli, S., Chacon-Tanarro, A., Choudhury, R., Codella, C., Coutens, A., Dulieu, F., Feng, S., Rimola, A., Hily-Blant, P., Holdship, J., Jimenez-Serra, I., Laas, J., Lefloch, B., Oya, Y., Podio, L., Pon, A., Punanova, A., Quenard, D., Sakai, N., Spezzano, S., Taquet, V., Testi, L., Theulé, P., Ugliengo, P., Vastel, C., Vasyunin, A. I., Viti, S., Yamamoto, S., Wiesenfeld, L., Fontani, F., Ceccarelli, C., Favre, C., Caselli, P., Neri, R., Sims, I. R., Kahane, C., Alves, F. O., Balucani, N., Bianchi, E., Caux, E., Jaber, Al-Edhari, A., Lopez-Sepulcre, A., Pineda, J. E., Bachiller, R., Bizzocchi, L., Bottinelli, S., Chacon-Tanarro, A., Choudhury, R., Codella, C., Coutens, A., Dulieu, F., Feng, S., Rimola, A., Hily-Blant, P., Holdship, J., Jimenez-Serra, I., Laas, J., Lefloch, B., Oya, Y., Podio, L., Pon, A., Punanova, A., Quenard, D., Sakai, N., Spezzano, S., Taquet, V., Testi, L., Theulé, P., Ugliengo, P., Vastel, C., Vasyunin, A. I., Viti, S., Yamamoto, S., and Wiesenfeld, L.

Abstract

The interstellar delivery of carbon atoms locked into molecules might be one of the key ingredients for the emergence of life. Cyanopolyynes are carbon chains delimited at their two extremities by an atom of hydrogen and a cyano group, meaning that they could be excellent reservoirs of carbon. The simplest member, HC3N, is ubiquitous in the galactic interstellar medium and found also in external galaxies. Thus, understanding the growth of cyanopolyynes in regions forming stars similar to our Sun, and what affects them, is particularly relevant. In the framework of the IRAM/NOEMA Large Program SOLIS (Seeds Of Life In Space), we have obtained a map of two cyanopolyynes, HC3N and HC5N, in the protocluster OMC-2 FIR4. Because our Sun is thought to be born in a rich cluster, OMC-2 FIR4 is one of the closest and best known representatives of the environment in which the Sun may have been born. We find a HC3N/HC5N abundance ratio across the source in the range 1..30, with the smallest values (≤10) in FIR5 and in the eastern region of FIR4. The ratios ≤10 can be reproduced by chemical models only if: (1) the cosmic-ray ionisation rate is ∼4× 10-14 s-1; (2) the gaseous elemental ratio C/O is close to unity; and (3) oxygen and carbon are largely depleted. The large is comparable to that measured in FIR4 by previous works and was interpreted as due to a flux of energetic (≥10 MeV) particles from embedded sources. We suggest that these sources could lie east of FIR4 and FIR5. A temperature gradient across FIR4, with T decreasing from east to west by about 10 K, could also explain the observed change in the HC3N/HC5N line ratio, without the need of a cosmic ray ionisation rate gradient. However, even in this case, a high constant cosmic-ray ionisation rate (of the order of 10s s-1) is necessary to reproduce the observations. © ESO 2017.

Published
2017

31. THE 2014 KIDA NETWORK FOR INTERSTELLAR CHEMISTRY

Author

Wakelam, V., primary, Loison, J.-C., additional, Herbst, E., additional, Pavone, B., additional, Bergeat, A., additional, Béroff, K., additional, Chabot, M., additional, Faure, A., additional, Galli, D., additional, Geppert, W. D., additional, Gerlich, D., additional, Gratier, P., additional, Harada, N., additional, Hickson, K. M., additional, Honvault, P., additional, Klippenstein, S. J., additional, Picard, S. D. Le, additional, Nyman, G., additional, Ruaud, M., additional, Schlemmer, S., additional, Sims, I. R., additional, Talbi, D., additional, Tennyson, J., additional, and Wester, R., additional

Published
2015
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32. Polycyclic aromatic hydrocarbons, carbon nanoparticles and the diffuse interstellar bands - Discussion

Author

Sarre, P., Crovisier, Kaiser, R. I., Chakrabarti, S., Richards, A. M. S., van Dishoeck, E. F., Herbst, E., Rowe, B. R., Semenov, D. A., Owen, T. C., Balucani, Nadia, Minard, R. D., Ehrenfreund, P., Kallenbach, R., Matthews, C., Smith, I. W. M., Sims, I. R., Mitchell, J. B. A., Wickham, A. J., de Bergh, C. M., Lintott, C. J., Dalgarno, A., Le Picard, S., Berteloite, C., Canosa, A., Black, J. H., Pino, T., Duley, W. W., Brechignac, P., Cox, N. L. J., Biennier, L., and Linnartz, H.

Subjects
astrochimica
Published
2006

33. Rotational energy transfer in collisions between CO(X singlet sigma plus, v=2, J=0, 1,4, and 6) and He at temperatures from 294 to 15 K

Author

Carty, D., Goodard, A., Sims, I. R., and Smith, I. W. M.

Abstract

Infrared-vacuum ultraviolet double resonance experiments have been implemented in the ultracold environment provided by a Cinétique de Réaction en Ecoulement Supersonique Uniforme apparatus. With this technique rate coefficients of two kinds have been measured for rotational energy transfer in collisions between CO and He: (a) those for total removal from the selected rotational states J = 0, 1, 4, and 6 in the vibronic state X 1+, v = 2, and (b) those for transfer between selected initial and specific final states. Using different Laval nozzles, results have been obtained at several different temperatures: 294, 149, 63, 27, and 15 K. The thermally averaged cross sections for total removal by collisions with He show only slight variations both with initial rotational state and with temperature. The variation of state-to-state rate coefficients with J show several general features: (i) a decrease with increasing J; (ii) a propensity to favor odd J over even J; and (iii) at lower temperatures, the distribution of rate coefficients against J becomes narrower, and decreases in J are increasingly favored over increases in J, a preference which is most strongly seen for higher initial values of J. The results are shown to be in remarkably good agreement with those obtained in ab initio scattering calculations by Dalgarno and co-workers [Astrophys. J. 571, 1015 (2002)].

Published
2004

34. Ultra-low temperature kinetics of neutral–neutral reactions: The reaction CN+O2 down to 26 K.

Author

Sims, I. R., Queffelec, J. L., Defrance, A., Rebrion-Rowe, C., Travers, D., Rowe, B. R., and Smith, I. W. M.

Subjects
*DYNAMICS, *CHEMICAL reactions, *CHEMISTRY
Abstract

A new method is described which enables the measurement for the first time of the rates of neutral–neutral gas-phase reactions at temperatures down to 26 K (and in the future, below). Results for the reaction of CN radicals with O2 are presented and discussed in terms of current theoretical treatments. [ABSTRACT FROM AUTHOR]

Published
1992
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35. A KINETIC DATABASE FOR ASTROCHEMISTRY (KIDA)

Author

Wakelam, V., primary, Herbst, E., additional, Loison, J.-C., additional, Smith, I. W. M., additional, Chandrasekaran, V., additional, Pavone, B., additional, Adams, N. G., additional, Bacchus-Montabonel, M.-C., additional, Bergeat, A., additional, Béroff, K., additional, Bierbaum, V. M., additional, Chabot, M., additional, Dalgarno, A., additional, van Dishoeck, E. F., additional, Faure, A., additional, Geppert, W. D., additional, Gerlich, D., additional, Galli, D., additional, Hébrard, E., additional, Hersant, F., additional, Hickson, K. M., additional, Honvault, P., additional, Klippenstein, S. J., additional, Le Picard, S., additional, Nyman, G., additional, Pernot, P., additional, Schlemmer, S., additional, Selsis, F., additional, Sims, I. R., additional, Talbi, D., additional, Tennyson, J., additional, Troe, J., additional, Wester, R., additional, and Wiesenfeld, L., additional

Published
2012
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40. General Discussion

Author

Ali, A., Mccoustra, M. R. S., Lambert, J. F., Acharyya, K., Visser, R., Kallenbach, R., Mautner, D., Yates, J. A., Al Halabi, A., Plane, J. M. C., Brown, W. A., Collings, M. P., Dulieu, F., Oberg, K. I., Rawlings, J. M. C., Vidali, G., Herbst, E., Palumbo, M. E., Fillion, J. H., Mason, N. J., Mitchell, J. B. A., Viti, S., Chakrabarti, S., Sims, I. R., Sabbah, H., Biennier, L., Smith, I. W. M., Minard, R. D., Goumans, T. P. M., Pilling, M. J., Faure, A., Casavecchia, Piergiorgio, Balucani, Nadia, Costes, M., Kaiser, R. I., Linnartz, H., Geppert, W. D., Semenov, D. A., Talbi, D., Loison, J. C., Quan, D. H., and Heard, D. E.

Subjects
Physical and Theoretical Chemistry, chimica del mezzo interstellare
Published
2006
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43. Rate coefficients for the reactions of C($\mathsf{^3}$P$\mathsf{{\it _J}}$) atoms with C2H2, C2H4, CH3C$ \mathsf{\equiv} $CH and H2C$ \mathsf{=} $C$ \mathsf{=} $CH2at temperatures down to 15 K

Author

Chastaing, D., Le Picard, S. D., Sims, I. R., Smith, I. W. M., Chastaing, D., Le Picard, S. D., Sims, I. R., and Smith, I. W. M.

Abstract

Rate coefficients for the reactions of ground state carbon atoms, C(3PJ), with the four unsaturated hydrocarbons C2H2, C2H4, ${\rm CH_3C\equiv CH}$and ${\rm H_2C=C=CH_2}$have been measured at temperatures down to 15 K. The experiments have been performed in a continuous flow CRESU (Cinétique de Réaction en Écoulement Supersonique Uniforme) apparatus using pulsed laser photolysis of C3O2to generate C(3PJ) atoms and laser-induced fluorescence in the vacuum ultraviolet to observe the kinetic decays of the atoms and hence determine the rate coefficients. All four reactions are found to occur at rates close to the collision-determined limit and the rates show at most a very mild dependence on temperature. It is argued that normally these reactions proceed along a reaction path with no barrier to form a strongly bound energised adduct, which subsequently eliminates an H atom to form the reaction products. The rates of the reactions of C(3PJ) atoms with larger unsaturated hydrocarbons are discussed. Finally, the relevance of the results for the chemistry of dense interstellar clouds is considered.

Published
2001
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47. General discussion

Author

Balint-Kurti, G. G., primary, Herbst, E., additional, Yamashita, K., additional, van Lenthe, J. H., additional, Smith, M. A., additional, Simons, J. P., additional, Gerlich, D., additional, Nenner, I., additional, Tennyson, J., additional, Plane, J. M. C., additional, Clary, D. C., additional, Smith, I. W. M., additional, Sims, I. R., additional, Stolte, S., additional, Nyman, G., additional, Millar, T. J., additional, Dalgarno, A., additional, Pilling, M. J., additional, Leach, S., additional, Canosa, A., additional, Tosi, P., additional, Demuynck, C., additional, Larsson, M., additional, Oka, T., additional, and Miller, S., additional

Published
1993
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48. INSIGHTS INTO THE CONDENSATION OF PAHS IN THE ENVELOPE OF IRC +10216.

Author

Biennier, L., Sabbah, H., Klippenstein, S. J., Chandrasekaran, V., Sims, I. R., and Rowe, B. R.

Subjects
POLYCYCLIC aromatic hydrocarbons, NUCLEATION, CIRCUMSTELLAR matter, THERMODYNAMICS, GAS phase reactions
Abstract

The mechanisms of nucleation and growth of carbon dust particles in circumstellar envelopes of carbon-rich stars in the red giant and AGB phases of their evolution are poorly understood. It has been proposed that the transition of gas phase species to solid particles, is achieved by the formation of a critical nucleus composed of two PAHs held together by van der Waals forces. Some insights into the validity of the nucleation of PAH molecules in the envelope can be gained through the investigation of the thermodynamics of dimers, representing the first stage towards condensation. We have performed experiments to identify the temperature range over which small PAH clusters form in saturated uniform supersonic flows. The kinetics of the formation has also been investigated. The experimental data have been combined with theoretical calculations. We unambiguously demonstrate that the association of small PAHs such as pyrene (C16H10) is slower than the destruction of the dimer in warm and hot environments such as IRC +10216. Our findings challenge a formation model based on the physical stacking of small PAH units in circumstellar shells of carbon rich stars. [ABSTRACT FROM AUTHOR]

Published
2011
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50. C + C<INF>2</INF>H<INF>2</INF>: A Key Reaction in Interstellar Chemistry

Author

Clary, D. C., Buonomo, E., Sims, I. R., Smith, I. W. M., Geppert, W. D., Naulin, C., Costes, M., Cartechini, L., and Casavecchia, P.

Abstract

The fast reaction between C(3P) and C2H2 is thought to be an important process in dense interstellar clouds as it provides a mechanism for the growth of carbon chains. This feature article describes a complementary series of recent experimental and theoretical investigations on this reaction. This includes kinetic measurements of rate constants at low temperatures and crossed molecular beam determinations of integral and differential cross sections. The theory employs first-principles electronic structure computations and wave packet dynamics to calculate cross sections and rate constants for forming the linear and cyclic isomers of C3H which can be formed in the reaction. The rate constant and cross section measurements show that there are no barriers in the potential surface for the reaction, whereas the differential cross section experiments provide new evidence for the formation of C3 + H2 products. The theoretical results of overall rate constants and cross sections agree quite well with the experiments, and it is predicted that the linear isomer of C3H should be formed preferentially at low temperatures.

Published
2002
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