Gas-phase thermochemistry

Although the kinetic method as a thermochemical tool has been debated, it is ultimately a refined bracketing approach, using branching ratios to interpolate a more precise location of the thermochemical property (as opposed to jnst between those of HA and HC). Therefore, the kinetic method should be at least as reliable as bracketing for the measnrement of gas-phase thermochemistry. The kinetic method has a... 

Armentrout, R B., Kickel, B. L., 1996, Gas-Phase Thermochemistry of Transition Metal Ligand Systems Reassessment of Values and Periodic Trends in Organometallic Ion Chemistry, Freiser, B. S. (ed.), Kluwer, Amsterdam. 

BAC-MP4 method Coupled-cluster calculations Gas-phase thermochemistry Equilibrium Gas-phase mechanisms... 

Our first example that attempts to imravel this complexity is entitled Gas-Phase Thermochemistry and Mechanism of Organometallic Tin Oxide CVD Precursors . The authors, M. Allendorf and A.M.B. van Mol, describe the development of quantum chemistry methods that can predict heats of formation for a broad range of tin compounds in the gas phase, which need to be considered when Sn(CH3)4 or (CH3)2SnCl2 and other tin alkyls are used as precursors together with oxygen and water for tin oxide deposition. 

Gas-Phase Thermochemistry and Mechanism of Organometallic Tin Oxide CVD Precursors... 

In some cases, a literature source of thermodynamic data may exist, allowing one to perform the conversion. Fortunately, standard references (such as Refs. 168 and 180) frequently tabulate both the condensed and gas phase thermochemistry values. When that is not the case, the following relations may be used, where the enthalpies and entropies of vaporization and fusion must be at 25 °C ... 

ENERGY RESOLVED CID VIA GUIDED ION BEAM EXPERIMENTS. Guided ion beam experiments have been used to measure a wealth of gas-phase thermochemistry [23]. Because these experiments measure thresholds for fragmentation, they can be probes of the activation energy [24]. 

One final method for deriving gas-phase thermochemistry of hypervalent ions does not involve gas-phase experiments at all. It requires measuring solid-state heats of formation of ionic salts and correcting to gas-phase values using calculated lattice energies for these salts. Since the lattice energies are in the vicinity of 1000 kJ/mol, 1% accuracy on these values is necessary to derive gas-phase thermochemistry with error limits of ca. 10 kJ/mol. This accuracy has yet to be met in practice. ... 

A knowledge of the gas-phase thermochemistry of ions and neutrals is important in mass spectrometry. This is particularly true for those ionization techniques (such as Cl) involving proton transfer reactions in the gas phase which result in the formation of pseudomol-... 

Of course, the gas-phase thermochemistry of ions is not solely restricted to the measurement of the quantities described above a wide range of other ion affinities have been measured, including methyl cation affinities, hydride affinities and halide affinities . Further, such measurements can often be related to unknown neutral thermochemistry via the appropriate thermochemistry cycle. For example, the phosphorus-carbon double bond strength (the sum of the a and n bond contributions) in HP=CH2 was recently estimated via mass spectrometric measurements to be 101 7 kcaF (ref. 43). 

Gas-Phase Thermochemistry of Organometallic and Coordination Complex Ions... 

The important catalytic applications of transient metal sulfides have motivated the study of the gas-phase thermochemistry of the early cationic transition-metal sulfides of the second row YS, ZrS and NbS [243] by guided ion-beam and ion-cyclotron resonance mass spectrometry. 

Notably, the observation of inverted lithium-sodium electronegativities by computations had been motivated by pecuhar anomahes in the gas-phase thermochemistry of the group 1 elements [65]. 

This chapter is restricted to gas-phase thermochemistry. In condensed phases (solutions, surfaces, etc.) medium effects may be small, so that the gas-phase values are often useful in condensed-phase work, at least as a... 

Sample results and approximate computational times for various computations of gas-phase thermochemistry... 

Gapeev A, Dunbar RC. Cation-ir interactions and the gas-phase thermochemistry of the Na+/phenylalanine complex. JAm Chem Soc. 2001 123 8360-5. 

The gas-phase thermochemistry of the halide anions X (F,Cl,Br,I) with a given MH sample molecule is highly dependent on the halide anion radius. For... 

Annentrout, P.B., Kickel, B.L., 1996. Gas-phase thermochemistry of transition metal ligand systems reassessment of values and periodic trends. In Preiser, B.S. (Ed.), Organometallic Ion Chemistry, vol. 15. Springer, Netherlands, p. 1. 

The CCCBDB is currently the only computational chemistry or physics database of its kind. This is due to the maturity of quantum mechanics to reliably predict gas-phase thermochemistry for small (20 nonhydrogen atoms or less), primarily organic, molecules, plus the availability of standard-reference-quality experimental data. For gas-phase kinetics, however, only in the past two years have high-quality (<2% precision) rate-constant data become available for H and OH transfer reactions to begin quantifying uncertainty for the quantum mechanical calculation of reaction barriers and tunneling. There is a critical need for comparable quality rate data and theoretical validation for a broader class of gas-phase reactions, as well as solution phase for chemical processing and life science, and surface chemistry. 

Nizzi KE, Pommerening CA, Sundta-lin LS (1998) Gas-phase thermochemistry of polyhalide anions. J Phys Chem A 102 7674... 

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