Interactions between naphthenic acids; dependence on molecular structure revealed through statistical analysis of ultra-high-resolution electrospray mass spectra.

Negative-ion electrospray mass spectra of samples of naphthenic acids contain peaks due to monomeric species [M-H](-) and dimeric species [2M-H](-). Working with a model system, intensities of the dimers were related to the intensities of monomers through linear inverse modelling. The statistical approaches investigated and the details of their applications to naphthenic acids are described here.

Throwing light on petroleum: simulated exposure of crude oil to sunlight and characterization using atmospheric pressure photoionization fourier transform ion cyclotron resonance mass spectrometry.

The change in profile of crude oil following a release into the environment is a topic of significant interest, and there is a need to develop analytical methodologies for understanding natural processes which affect related complex mixture profiles. One such process is the exposure to sunlight. In the following investigation, three oil samples were studied: one served as a control, a second was subjected to irradiation by an ultraviolet lamp, and a third sample was irradiated by a SoLux light source which closely models the solar emission profile.

Electronic spectroscopy of toluene-rare-gas clusters: the external heavy atom effect and vibrational predissociation.

Toluene-X van der Waals clusters (where X = Ne, Ne2, Ar, Ar2, Kr, Xe) have been investigated by fluorescence excitation spectroscopy in the region of the S1-S0 transition. With the exception of Xe, for each rare-gas studied, we have assigned cluster transitions in the region of all the strong monomer vibrational bands up to 1000 cm(-1) above the origin band. We have further investigated the S1 relaxation dynamics for each vibrational level of each complex, via their fluorescence decay profiles.

A combined experimental and computational investigation of the microscopic external heavy atom effect in van der Waals clusters.

We present a combined experimental and computational study of the external heavy atom effect in van der Waals clusters of para-difluorobenzene (pDFB) with rare-gas atoms. Experimentally, clustering with rare-gas atoms is observed to shorten significantly the S1 fluorescence lifetime compared with that of the pDFB monomer, an effect we interpret in terms of an enhancement of the S1-T1 intersystem crossing rate. In order to test the validity of this widely held assumption, we have calculated the S1-T1 spin-orbit coupling matrix elements in the X-pDFB complexes (X=Ne, Ar, Kr) using a multiconfigurational linear response approach.