Population distributions in the vibrational deactivation of benzene and benzene-d6. First and second moments derived from two-color infrared fluorescence measurements

Time-resolved two-color infrared fluorescence (IRF) from highly vibrationally excited benzene and benzene-d6 has been used to determine means and variances of the excited molecule population distributions over the majority of the energy range during deactivation via collisional energy transfer to unexcited molecules. These measurements extend the IRF technique to produce information about the first two moments of energy transfer induced population distributions present during the collisional deactivation process. A simple means of analysis of IRF from multiple emission bands is presented, which in principle yields information about higher moments, as well as increasingly precise determination of lower moments. Results from this analysis are independent of any assumed models for collisional energy transfer. In the experiments, simultaneous monitoring of IRF from the C---H (C---D) stretching mode fundamental region at [approximate]3060 cm-1 ([approximate]2290 cm-1) and first overtone region at [approximate]6000 cm-1 ([approximate]4500 cm-1), allows independent observation of two subsets of the total population of excited molecules, each containing the vibrational energy required to emit photons in the observed bands. Similar results are obtained from analysis of the time- and wavelength-resolved [Delta][nu]= -1 C---H stretch emission spectrum of highly excited benzene-h6 as it is deactivated by collisions. The two-color results are shown to provide meaningful information about the first two moments of the energy population distribution over much of the energy range. Knowledge of the population distribution is important since it results directly from the form of Pc(E', E), the step size probability distribution function for collisional energy transfer. Master equation simulations are used together with these results in order to derive some limitations on the possible forms of Pc(E', E).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30588/1/0000225.pd

Glutamate receptor blockade alters the development of intracortical connections in rat barrel cortex

We tested the hypothesis that glutamate receptor mediated activity is required for the postnatal development of intracortical connections in layers II/III of rodent barrel cortex. To block glutamate receptors, a slow release polymer (elvax) loaded with a glutamate receptor antagonist (D-AP5) was targeted subdurally over the future rat barrel cortex on P0 (day of birth). On P14-16 biotinylated dextran amine (BDA) was injected under the elvax into all layers to label neurons retrogradely. A BDA injection was made stereotactically at the mirror site of the untreated hemisphere of each animal. The animals survived to P22-24. Injection sites and retrogradely labeled cell bodies were identified in tangential sections in relation to the barrel map. D-AP5 treated and untreated hemispheres were matched according to the location of the injection site in the barrel map. Glutamate receptor blockade did not prevent the growth of intrinsic projections, but altered their organization. The normal row-like asymmetry of connections in untreated hemispheres was lacking in the D-AP5 treated cortex (ANOVA, p =0.02). Cortical activity mediated through glutamate receptors contributes to the correct development of connections between barrel columns in layers II/III