A quasiclassical trajectory study of energy transfer in benzene-benzene collisions A classical trajectory study of collisional energy transfer in thermal unimolecular reactions Quasiclassical trajectory calculations of the energy transfer of highly vibrationally excited benzene and hexafluorobenzene ͑HFB͒ molecules colliding with helium, argon and xenon have been performed. Deactivation is found to be more efficient for HFB in accord with experiment. This effect is due to the greater number of low frequency vibrational modes in HFB. A correlation between the energy transfer parameters and the properties of the intramolecular potential is found. For benzene and HFB, average energies transferred per collision in the given energy range increase with energy. Besides weak collisions, more efficient ''supercollisions'' are also observed for all substrate-bath gas pairs. The histograms for vibrational energy transfer can be fitted by biexponential transition probabilities. Rotational energy transfer reveals similar trends for benzene and HFB. Cooling of rotationally hot ensembles is very efficient for both molecules. During the deactivation, the initially thermal rotational distribution heats up more strongly for argon or xenon as a collider, than for helium, leading to a quasi-steady-state in rotational energy after only a few collisions.

Tripeptides comprising amino acids with neutral side chains interact with alkaline earth metal ions to form gas-phase anionic complexes of the composition [tripept + Met2"1" -3H+]" under fast atom bombardment. The metal ion binds to the deprotonated C-terminal carboxylate group and to the two amide nitrogens. Because the C-terminal and the central amino acid are tightly bound by the metal ion, they are not vulnerable to collisionally activated decompositions in a tandem mass spectrometer. Instead, the significant fragmentations occur at the N-terminal amino acid site, which is the least tightly bonded. Ions are formed by elimination of an imine and the imine plus CO from the N-terminus (product ions are assigned as x2 + H and y2, respectively). Other major fragmentations of this complex include dehydrogenation and loss of an ammonia molecule. Peptides with functionalized side chains, such as those of serine, threonine, and phenylalanine, lose the side chains readily when they are bound to metal ions and submitted to collisional activation. Other fragmentation channels are largely suppressed, indicating direct metal ion-side chain interaction. Fragmentation mechanisms are proposed on the basis of results with isotopically labeled peptides and from MS/MS/MS experiments.

The average energy transferred per collision and its dependence on collision duration were evaluated by using quasiclassical trajectory calculations with valance force field intramolecular potential for toluene and pairwise Lennard-Jones intermolecular potential for argon-toluene interactions. The average energy transferred in up, down, and overall collisions were sorted according to the duration of the collisions. It was found that, on average, collision durations, for collisions lasting longer than zero, are 0.68 and 0.23 ps at 300 and 1500 K, respectively, and this is the time in which energy transfer takes place. Most collisions of duration longer than 0 are impulsive, and the number of complex-forming collisions is negligible. The average minimal distance at which the collisional event manifests itself in internal energy change in the molecule is -0.31 nm at both 300 and 1500 K. One in 800 collisions is a supercollision. The implications of these findings on energy transfer models are discussed.

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The introduction of ninhydrin treatment as a chemical technique for the visualisation of latent fingermarks on porous surfaces revolutionised approaches to forensic fingermark examination. Since then, a range of amino acid sensitive reagents has been developed and such compounds are in widespread use by law enforcement agencies worldwide. This paper reviews the development and use of these reagents for the detection of latent fingermarks on porous surfaces. A brief overview is provided, including an historical background, forensic significance, and a general approach to the development of latent fingermarks on porous surfaces. This is followed by a discussion of specific amino acid sensitive treatments.