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171 results on '"Smith, I. W. M."'

1. Review of important reactions for the nitrogen chemistry in the interstellar medium

Author

Wakelam, V., Smith, I. W. M., Loison, J. -C., Talbi, D., Klippenstein, S. J., Bergeat, A., Geppert, W. D., and Hickson, K. M.

Subjects
Astrophysics - Galaxy Astrophysics
Abstract

Predictions of astrochemical models depend strongly on the reaction rate coefficients used in the simulations. We reviewed a number of key reactions for the chemistry of nitrogen-bearing species in the dense interstellar medium and proposed new reaction rate coefficients for those reactions. The details of the reviews are given in the form of a datasheet associated with each reaction. The new recommended rate coefficients are given with an uncertainty and a temperature range of validity and will be included in KIDA (http://kida.obs.u-bordeaux1.fr)., Comment: 39 pages, not published in refereed journal, datasheets are given in KIDA

Published
2013

2. 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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3. Reaction Networks For Interstellar Chemical Modelling: Improvements and Challenges

Author

Wakelam, V., Smith, I. W. M., Herbst, E., Troe, J., Geppert, W., Linnartz, H., Oberg, K., Roueff, E., Agundez, M., Pernot, P., Cuppen, H. M., Loison, J. C., and Talbi, D.

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes -- ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination -- is reviewed. Emphasis is placed on those reactions that have been identified, by sensitivity analyses, as 'crucial' in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust particles also influence the observed abundances of molecules in the interstellar medium. Their role is included in gas-grain, as distinct from gas-phase only, models. We review the methods for incorporating both accretion onto, and reactions on, the surfaces of grains in such models, as well as describing some recent experimental efforts to simulate and examine relevant processes in the laboratory. These efforts include experiments on the surface-catalysed recombination of hydrogen atoms, on chemical processing on and in the ices that are known to exist on the surface of interstellar grains, and on desorption processes, which may enable species formed on grains to return to the gas-phase., Comment: Accepted for publication in Space Science Reviews

Published
2010
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8. 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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9. Vibrational energy transfer in HBr–C2D2 mixtures.

Author

Breshears, W. D. and Smith, I. W. M.

Subjects
*FLUORESCENCE, *ENERGY transfer
Abstract

Infrared fluorescence from HBr and C2D2(ν3) has been measured following irradiation of HBr–C2D2 mixtures with a pulsed HBr laser. The fluorescence decay from both species yields the total rate constant for deactivation of HBr(v=1) by collisions with C2D2, k=(1.6±0.1)×104 s-1 Torr-1. The exponential rise of C2D2(ν3) fluorescence is characterized by the rate constants k=(3.4±0.2)×104 s-1 Torr -1 for collisions with both C2D2 and HBr, and k=(5.5±2.3)×103 s-1 Torr-1 for collisions with added Ar. A model developed to fit the observations implies that ν3 is populated indirectly by transfer from another, unidentified, level of C2D2, and that the exponential rise constants refer to transfer from ν3 to this level. [ABSTRACT FROM AUTHOR]

Published
1985
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11. 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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14. Kinetics of formation and thermodynamics of the elusive HOOO radical

Author

Le Picard, Sébastien D., Tizniti, Meryem, Canosa, André, Sims, Ian R, Smith, I. W. M., Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), and Brébion, Alice

Subjects
[PHYS]Physics [physics], Molecular physics, ComputingMilieux_MISCELLANEOUS, [PHYS] Physics [physics]
Abstract

International audience

Published
2010

15. Direct measurement of the binding energy of the weakly bound HO3 radical cluster

Author

Sims, Ian R, Canosa, André, Le Picard, Sébastien D., Tizniti, Meryem, Smith, I. W. M., Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), and Brébion, Alice

Subjects
[PHYS]Physics [physics], Molecular physics, [PHYS] Physics [physics]
Published
2010

18. 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

19. 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

20. 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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21. The relaxation of OH (v = 1) and OD (v = 1) by H2O and D2O at temperatures from 251 to 390 K

Author

McCabe, D. C., Rajakumar, B., Marshall, P., Smith, I. W. M., Ravishankara, A. R., McCabe, D. C., Rajakumar, B., Marshall, P., Smith, I. W. M., and Ravishankara, A. R.

Abstract

We report rate coefficients for the relaxation of OH(v = 1) and OD(v = 1) by H2O and D2O as a function of temperature between 251 and 390 K. All four rate coefficients exhibit a negative dependence on temperature. In Arrhenius form, the rate coefficients for relaxation (in units of 10–12 cm3 molecule–1 s–1) can be expressed as: for OH(v = 1) + H2O between 263 and 390 K: k = (2.4 ± 0.9) exp((460 ± 115)/T); for OH(v = 1) + D2O between 256 and 371 K: k = (0.49 ± 0.16) exp((610 ± 90)/T); for OD(v = 1) + H2O between 251 and 371 K: k = (0.92 ± 0.16) exp((485 ± 48)/T); for OD(v = 1) + D2O between 253 and 366 K: k = (2.57 ± 0.09) exp((342 ± 10)/T). Rate coefficients at (297 ± 1 K) are also reported for the relaxation of OH(v = 2) by D2O and the relaxation of OD(v = 2) by H2O and D2O. The results are discussed in terms of a mechanism involving the formation of hydrogen-bonded complexes in which intramolecular vibrational energy redistribution can occur at rates competitive with re-dissociation to the initial collision partners in their original vibrational states. New ab initio calculations on the H2O–HO system have been performed which, inter alia, yield vibrational frequencies for all four complexes: H2O–HO, D2O–HO, H2O–DO and D2O–DO. These data are then employed, adapting a formalism due to Troe (J. Troe, J. Chem. Phys., 1977, 66, 4758), in order to estimate the rates of intramolecular energy transfer from the OH (OD) vibration to other modes in the complexes in order to explain the measured relaxation rates—assuming that relaxation proceeds via the hydrogen-bonded complexes.

Published
2006

22. 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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26. 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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30. 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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35. General discussion

Author

Balint-Kurti, G. G., primary, Dalgarno, A., additional, Simons, J. P., additional, Flower, D., additional, Millar, T. J., additional, Smith, I. W. M., additional, van Dishoeck, E. F., additional, Williams, D. A., additional, Ubachs, W., additional, Eikema, K. S. E., additional, Levelt, P. F., additional, Stolte, S., additional, Hogervorst, W., additional, Rostas, F., additional, Thaddeus, P., additional, Black, J. H., additional, Walmsley, C. M., additional, Watson, J. K. G., additional, Leach, S., additional, Herbst, E., additional, Gerlich, D., additional, Duke, B. J., additional, Botschwina, P., additional, Kroto, H., additional, Husain, D., additional, Clary, D. C., additional, Papoular, R., additional, Omont, A., additional, Nenner, I., additional, Kawaguchi, K., additional, Howe, D. A., additional, Oka, T., additional, Tennyson, J., additional, Allamandola, L. J., additional, and Gray, M. D., additional

Published
1993
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37. General discussion

Author

Smith, I. W. M., primary, Valentini, J. J., additional, Neumark, D. M., additional, Ashfold, M. N. R., additional, González, M., additional, Temps, F., additional, Laganà, A., additional, Alvariño, J. M., additional, Quintales, L. M., additional, Polanyi, J. C., additional, Grice, R., additional, Truhlar, D. G., additional, McKendrick, K. G., additional, Aoiz, F. J., additional, Mackay, R. S., additional, Xu, Q.-X., additional, Wu, V. W.-K., additional, Clary, D. C., additional, Soep, B., additional, Schatz, G., additional, Child, M. S., additional, Shapiro, M., additional, Zewail, A. H., additional, Metiu, H., additional, Plane, J. M. C., additional, Gerber, G., additional, Combariza, J. E., additional, Manz, J., additional, Paramonov, G. K., additional, Görtler, S., additional, Simons, J. P., additional, Morokuma, K., additional, Kolba, E., additional, Kosloff, R., additional, Sondermann, F., additional, Herrero, V. J., additional, Rábanos, V. Sáez, additional, Welge, K. H., additional, Girard, B., additional, Manolopoulos, D. E., additional, Casavecchia, P., additional, Balucani, N., additional, Beneventi, L., additional, Stranges, D., additional, Volpi, G. G., additional, Bowman, J. M., additional, Marcus, R. A., additional, Pack, R. T., additional, Parker, G. A., additional, Connor, J. N. L., additional, Chatfield, D. C., additional, Friedman, R. S., additional, Lynch, Ms. G. C., additional, Foster, R., additional, Frost, M. J., additional, Hippler, H., additional, Schlepegrell, A., additional, Troe, J., additional, Gericke, K.-H., additional, Alexander, M. H., additional, Dagdigian, P. J., additional, Clement, S. G., additional, Howe, J. D., additional, Western, C. M., additional, Dixon, R. N., additional, and Sarre, P. J., additional

Published
1991
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38. General discussion.

Author

Ureña, A. G., Simons, J. P., Wolfrum, J. W., Balint-Kurti, G. G., Clary, D. C., Zare, R. N., Truhlar, D. G., Smith, I. W. M., Pilling, M. J., Setser, D. W., Krümpelmann, T., Ottinger, Ch., Schechter, I., and Levine, R. D.

Published
1987
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39. General discussion.

Author

Farrar, J. M., Bowers, M. T., Leone, S. R., Gislason, E. A., Murrell, J. N., Braga, J. P., Dunne, L. J., Guo, H., Clary, D. C., Varandas, A. J. C., Smith, I. W. M., Rubahn, H-G., Sathyamurthy, N., and Toennies, J. P.

Published
1987
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40. General discussion.

Author

Grice, R., Schatz, G. C., Clary, D. C., Smith, I. W. M., Connor, J. N. L., Wolfrum, J., Truhlar, D. G., Laganà, A., Pack, R. T., Parker, G. A., McKendrick, K. G., Amaee, B., Whitehead, J. C., Jakubetz, W., Varandas, A. J. C., Schechter, I., and Levine, R. D.

Published
1987
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41. General discussion.

Author

Pacey, P. D., Dunning, T. H., Smith, I. W. M., Miller, W. H., Truhlar, D. G., Aquilanti, V., Laganà, A., Gervasi, O., Garcia, E., Kuntz, P. J., Menendez, M., Banares, L., Alonso, J., Urena, A. G., and Garrett, B. C.

Published
1987
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42. General discussion.

Author

Connor, J. N. L., Halberstadt, N., Ewing, G. E., Balint-Kurti, G. G., Kidd, I. F., Hutson, J. M., Beswick, J. A., Delgado-Barrio, G., Villareal, P., Mareca, P., Smith, I. W. M., Jouvet, C., Schaefer, J., Burton, P. G., Gough, T. E., Keil, M., Knight, D. G., Scoles, G., Geraedts, J., and Jortner, J.

Published
1982
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43. General discussion.

Author

Bly, S. H. P., Dickson, L. W., Nomura, Y., Polanyi, J. C., Smith, I. W. M., Clough, P. N., Kneba, M., Wellhausen, U., Wolfrum, J., Siska, P. E., Wolf, R. J., Sloane, C. S., Hase, W. L., Holmlid, L., Rynefors, K., Luther, K., Quack, M., Freed, K., Jackson, W. M., and Naaman, R.

Published
1979
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49. Reviews of books.

Author

Bosanac, S. D., Steele, D., North, A. M., Williams, R. J. P., Harriman, A., Smith, I. W. M., Rowlinson, J. S., Bodenhausen, G., Kettle, S. F. K., and Hillier, I. H.

Published
1983
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