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School of Chemistry, University of Nottingham,UK 1 Data, Data Everywhere! But Which of it to Use? The Need for Data Validation and Accountability in Laboratory.

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Presentation on theme: "School of Chemistry, University of Nottingham,UK 1 Data, Data Everywhere! But Which of it to Use? The Need for Data Validation and Accountability in Laboratory."— Presentation transcript:

1 School of Chemistry, University of Nottingham,UK 1 Data, Data Everywhere! But Which of it to Use? The Need for Data Validation and Accountability in Laboratory Astrochemistry Martin McCoustra

2 School of Chemistry, University of Nottingham,UK 2  A Difficult Topic –Apologies  What is Needed in Data Terms? –Spectroscopic Data –Kinetic Data  Drawing an Analogy –Atmospheric Chemistry  Where Do We Go From Here? Outline

3 School of Chemistry, University of Nottingham,UK 3 A Difficult Topic For Discussion? Astrochemistry Spectroscopy and Theory Chemical Intuition Observational Astronomy Reaction Rate Measurements

4 School of Chemistry, University of Nottingham,UK 4 A Difficult Topic For Discussion?  Laboratory data are crucial for Astrochemistry –Previous presentations at this Workshop –White Paper from NASA’s 2002 Laboratory Astrophysics Workshop –Review and foresight articles in the literature for example, J. M. Greenberg, Surf. Sci., 2002, 500, 793,D. A. Williams and E. Herbst, Surf. Sci., 2002, 500, 823,T. E. Madey, R. E. Johnson and T. M. Orlando, Surf. Sci., 2001, 500, 838. But Can We Trust the Quality of the Data?

5 School of Chemistry, University of Nottingham,UK 5 What Types Of Data Are Needed? Astrochemical Data  Spectroscopic Data –Identification –Wavelengths ranging from the X-ray to radio –Measurements made with increasingly higher resolution –Wide range of chemical species in both the gas and solid phases  Reaction Rate Data –Mechanistic data supports identification –Rate data are essential for modelling chemical change –Not the normal reaction conditions

6 School of Chemistry, University of Nottingham,UK 6 What Types Of Data Are Needed? Spectroscopic Data  Laboratory Measurements –Need to work to resolutions to match or better observations –Need to be aware of the impact of data processing on the data –Look towards a common format for data exchange e.g. JCAMP  Theoretical Calculations –Very effective for isolated (gas phase) species –Solids are challenging Crystalline,DFT (e.g. CASTEP) and periodic HF calculations (e.g. Crystal98) Amorphous,Cluster Calculations? MM-QM Combinations?

7 School of Chemistry, University of Nottingham,UK 7 What Types Of Data Are Needed?  Solid Phase CO as an illustrative example LO Mode 2143 cm -1 TO Mode 2139 cm -1 –Grazing-incidence RAIR spectroscopy from a metal substrate is sensitive to only one plane of polarisation of the IR light –Increasing resolution clearly shows a splitting of the solid CO stretching vibration

8 School of Chemistry, University of Nottingham,UK 8 What Types Of Data Are Needed? –Observation of splitting may be indicative of a polarised IR source –Recent work from Pontoppidan et al. (Astron. Astrophys., submitted) suggests this might be the case in some objects LOTO  Solid Phase CO as an illustrative example

9 School of Chemistry, University of Nottingham,UK 9 What Types Of Data Are Needed? Reaction Rate Data  Laboratory Measurements –Reaction rates and their temperature dependence from 10 K to over 1000 K –Photon and charged particle interaction cross- sections –Environment where dynamics is important –Gases, solids and surfaces  Theoretical Calculations –An excellent tool for investigating dynamical effects –Less useful for evaluating thermal reaction rates especially on surfaces and in the solid phase

10 School of Chemistry, University of Nottingham,UK 10 What Types Of Data Are Needed?  Temperature dependence of rate of the CN + C 2 H 6 reaction as an illustrative example –It is common for high temperature (>250 K) rate data to fit the Arrhenius expression Courtesy of Dr. Ian SIms –But extrapolation to lower temperature can be unreliable!!!!

11 School of Chemistry, University of Nottingham,UK 11 What Types Of Data Are Needed?  Temperature dependence of rate of the CN + C 2 H 6 reaction as an illustrative example –It is common for high temperature (>250 K) rate data to fit the Arrhenius expression –But extrapolation to lower temperature can be unreliable!!!! Courtesy of Dr. Ian SIms

12 School of Chemistry, University of Nottingham,UK 12 What Types Of Data Are Needed?  Temperature dependence of rate of the CN + C 2 H 6 reaction as an illustrative example –It is common for high temperature (>250 K) rate data to fit the Arrhenius expression –But extrapolation to lower temperature can be unreliable!!!! Courtesy of Dr. Ian SIms

13 School of Chemistry, University of Nottingham,UK 13 What Types Of Data Are Needed?  Thermal desorption of water ice as an illustrative example –Measurements of both activation energy and pre- exponential factor for desorption are required –Care must be taken with reaction orders on surfaces –Fraser et al., Mon. Not. Roy. Astron. Soc., 2001, 327, 1165

14 School of Chemistry, University of Nottingham,UK 14 What Types Of Data Are Needed?  Thermal desorption of water ice as an illustrative example –Solid films exhibit zero order desorption kinetics –But monolayers or less may exhibit first or second order desorption –This impacts on when the film material will reappear in the gas phase

15 School of Chemistry, University of Nottingham,UK 15 Where Do We Find This Data?  Primary Literature –For the most part, chemical data comes from the extensive (!!!!) chemical literature but you may have to think “out of the box” to find it  Database Compilations –NIST Databases, Leiden Solid State Spectral Database, UMIST Kinetics Database –Issues of database accuracy and maintenance –“Proprietary” information  Chinese Whispers Can Anything Make Life Simpler?

16 School of Chemistry, University of Nottingham,UK 16 Drawing An Analogy  Astrochemistry –Chemical processes coupled with physical processes –Chemical reactions in an environment where there is energy, mass and momentum transport –Driven by radiation from stars  Atmospheric Chemistry –Chemical processes coupled with physical processes –Chemical reactions in an environment where there is energy, mass and momentum transport –Driven by radiation from a star (solar radiation) In the Broadest Sense, Much More Alike Than Different!

17 School of Chemistry, University of Nottingham,UK 17 Drawing An Analogy  Spectroscopic Data –Many of the same sources as for astrochemistry but additional national atmospheric chemistry databases  Reaction Rate Data –A solution to the problem of hunting for data and being assured of its quality How Does Atmospheric Chemistry Solve its Data Needs?

18 School of Chemistry, University of Nottingham,UK 18 Drawing An Analogy  An international committee established as part of the IUPAC Division on Physical Chemistry Commission on Chemical Kinetics –Professor R. Atkinson (Riverside, California, USA) Professor D. L. Baulch (Leeds, UK), Dr. R. A. Cox (Cambridge, UK), Dr. John Crowley (MPI for Chemistry, Mainz, Germany), Dr. R. F. Hampson (NIST, USA), Dr. M. E. Jenkin (Imperial College, UK), Professor J. A. Kerr (Birmingham, UK), Dr. M. J. Rossi (EPFL, Lausanne, Switzerland), Professor J. Troe (Göttingen, Germany)

19 School of Chemistry, University of Nottingham,UK 19 Drawing An Analogy  An international committee established as part of the IUPAC Division on Physical Chemistry Commission on Chemical Kinetics –Chemical expertise and intuition applied to the collation of chemical rate data for use in atmospheric chemistry –Publishes compilations of evaluated data on a regular basis in the Journal of Physical and Chemical Reference Data and on the web –“Certainty” in the data means that atmospheric modelling can focus more on the physics of the problem

20 School of Chemistry, University of Nottingham,UK 20 Drawing An Analogy  The reaction HO+H 2 as an illustrative example –Review the literature to collate existing data –Recommend a preferred value to the user community with a justification

21 School of Chemistry, University of Nottingham,UK 21 Drawing An Analogy  The interaction of H 2 O with solid surfaces as an illustrative example –Review not just homogeneous but heterogeneous data in the collation of existing data –In some cases, recommendation remains a little open but at least all the relevant data is presented

22 School of Chemistry, University of Nottingham,UK 22 Where Do We Go From Here?  Data evaluation in the IUPAC model reduces uncertainty in the use of data –Users can focus on the use of the data and the physics of their problems rather than worrying about data quality –But it isn’t a panacea!!! Remember the example of heterogeneous chemistry!!! –Use of the UMIST Kinetics Database across the community goes someway towards this –But there may be issues with evaluation of the content of that database and with its maintenance

23 School of Chemistry, University of Nottingham,UK 23 Where Do We Go From Here?  Do we need a community-based effort that applies the IUPAC data evaluation model to the maintenance of the UMIST database?  How would we support this? –National Research Councils NO… Danger of data becoming “proprietary”? –Space agency (NASA/ESA/...) funding Their science needs it, so should they fund it? –IAU/IUPAC Clearly the role of IAU Commission No. 14 on Atomic and Molecular Data but why duplicate the IUPAC effort?

24 School of Chemistry, University of Nottingham,UK 24 Where Do We Go From Here? Open the Discussion to the Floor


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