Older work using classical trajectory calculations had shown that for the isomerisation of CNCN --> NCCN, recrossing of the potential barrier appeared to persist for periods exceeding the characteristic IVR relaxation time.

An improved potential energy surface for this reaction has been constructed, with close attention to the vicinity of the potential barrier to avoid the chance of trajectories being accidentally trapped by a spurious dip in the saddle-point region.

New trajectory calculations show that these recrossings come in bursts of up to 10, spaced about 0.1 ps apart, and a similar effect is found for the MeNC --> MeCN reaction. Thus, when a trajectory enters the transition region, it has an equal probability of going on to product or returning to reactant, causing the transition state theory transmission coefficient to be exactly 0.5; this is similar to the situation predicted by M.Polanyi in 1932 for the H + H2 exchange reaction.

References

1. DeLin Shen and H.O.Pritchard, Randomisation and isomerisation rate constants for isocyanogen.
   J.C.S. Faraday Transactions, 92, 4357-4360 (1996).
2. H.O.Pritchard, S.R.Vatsya and DeLin Shen, Distribution of vibrational potential energy in molecular systems.
   J.Chem.Phys., 110, 9384-9389 (1999).
3. H.O.Pritchard, Recrossings and transition state theory.  J.Phys.Chem.A, 109, 1400-1404 (2005).

Although our contract for experimental studies on the mechanisms by which free-radical initiators stimulate the spontaneous ignition of diesel fuel has expired, theoretical work using Gaussian molecular orbital calculations continues.

References

1. P.Q.E.Clothier, DeLin Shen and H.O.Pritchard. Stimulation of diesel-fuel ignition by benzyl radicals.
   Combustion and Flame, 101, 383-386 (1995).
2. P.Q.E.Clothier and H.O.Pritchard, Isolation of diesel-fuel ignition inhibitors in reverse micelles.
   Combustion and Flame, 119, 195-198 (1999).
3. P.Q.E.Clothier, S.M.Heck and H.O.Pritchard, Retardation of spontaneous hydrocarbon ignition in diesel engines by di-tert-butyl peroxide.
   Combustion and Flame, 121, 689-694 (2000).
4. Wai-To Chan, S.M.Heck and H.O.Pritchard, Reaction of nitrogen dioxide with hydrocarbons and its influence on spontaneous ignition. A computational study.
   Phys.Chem.Chem.Phys., 2, 56-62 (2001).
5. Wai-To Chan and H.O.Pritchard, Iso-nitrous acid. Spectroscopic frequencies and possible synthetic pathways.
   Phys.Chem.Chem.Phys., 3, 557--560 (2002).

Spontaneous ignition occurs in a wide variety of situations, including heaps of sawdust and wood chippings, raw-wool fleeces, rubbish dumps, etc. We have found that self-heating can occur in rubber-containing materials, raising the possibility that some tyre-dump (and perhaps other) fires could be have been due to spontaneous ignition.

References

1. P.C.Bowes, Self-heating: evaluating and controlling the hazards.
   H.M.Stationery Office, London, 1984.
2. P.Q.E.Clothier and H.O.Pritchard, Atmospheric oxidation and self-heating in rubber-containing materials.
   Combustion and Flame, 133, 207-210 (2003).
3. H.O.Pritchard, On the atmospheric oxidation of liquid toluene.
   Phys. Chem. Chem. Phys., 8, 4559-4562 (2006).

A new method for calculating extremely small eigenvalues has been tested and shown to be slightly more robust than the conventional Nesbet method. The new method appears to be capable of extension to two, or more, small eigenvalues, opening the possibility for reliable calculations on multi-channel unimolecular reactions.

References

1. H.O.Pritchard, Eigenvalue methods in unimolecular rate calculations.
   J.Phys.Chem.A, 108, 5249--5252 (2004).
2. H.O.Pritchard, Eigenvalue methods for unimolecular rate calculations with several products.
   J.Phys.Chem.A, 111, 10880--10883 (2007).

Rigorous calculation of energy content and carbon dioxide emission for various hydrocarbon and oxygenated transportation fuels.

References

1. H.O.Pritchard, Carbon dioxide versus energy balances for transportation fuels.
   Energy Environ. Sci., 2, 815--817 (2009).