On the Electronic Spectroscopy of Closed Shell Cations Derived From Resonance Stabilized Radicals: Insights From Theory and Franck-Condon Analysis

Context. Recent attention has been directed on closed-shell aromatic cations as potential carriers of the diffuse interstellar bands. The spectra of mass-selected, matrix-isolated benzylium, and tropylium cations were recently reported. The visible spectrum of benzylium exhibits a large Franck-Condon (FC) envelope, inconsistent with diffuse interstellar band carriers. Aims. We perform a computational analysis of the experimentally studied benzylium spectrum before extending the methods to a range of larger, closed-shell aromatic cations to determine the potential for this class of systems as diffuse interstellar band carriers. Methods. Density functional theory (DFT), time-dependant ((TD)DFT), and multi-configurational self-consistent field second-order perturbation theory (MRPT2) methods in concert with multidimensional FC analysis is used to model the benzylium spectrum. These methods are extended to larger closed-shell aromatic hydrocarbon cations derived from resonance-stabilized radicals, which are predicted to show strong S0 → Sn transitions in the visible region. The ionization energies of a range of these systems are also calculated by DFT. Results. The simulated benzylium spectrum was found to yield excellent agreement with the experimental spectrum showing an extended progression in a low frequency (510 cm-1) ring distortion mode. The FC progression was found to be significantly quenched in the larger species: 1-indanylium, 1-naphthylmethylium, and fluorenium. Excitation and ionization energies of the closed-shell cations were found to be consistent with diffuse interstellar band carriers, with the former lying in the visible range and the latter straddling the Lyman limit in the 13−14 eV range. Conclusions. Large closed-shell polycyclic aromatic hydrocarbon cations remain viable candidate carriers of the diffuse interstellar bands

Using teacher voices to develop the ASELL Schools professional development workshops

This article describes how the Advancing Science and Engineering through Laboratory Learning (ASELL) Schools program was developed. ASELL School's directive is to facilitate the embedding of inquirybased learning in secondary school classrooms through workshop-based teacher professional development (PD). The approach of ASELL Schools is to balance the lessons learned in education research with teacher voices and curriculum requirements in the design and implementation of teacher professional development. This has resulted in a unique workshop experience, where students and teachers work together on open-inquiry investigations. Afterward, teachers and students are separated for pedagogical sessions, and teachers are given time to discuss and share ideas. The discussion is focussed around the key ASELL Schools pedagogical tool, called the 'Inquiry Slider'. We outline an iterative process based on listening to teacher voices, which was used to develop the workshops. We also demonstrate that the Inquiry Slider is an effective pedagogical tool allowing teachers to focus and expand their efforts to bring more inquiry-based learning into their classrooms

Spectroscopy and Dynamics of the Predissociated, Quasi-linear S2 State of Chlorocarbene

In this work, we report on the spectroscopy and dynamics of the quasi-linear S2 state of chlorocarbene, CHCl, and its deuterated isotopologue using optical-optical double resonance (OODR) spectroscopy through selected rovibronic levels of the S1 state. This study, which represents the first observation of the S2 state in CHCl, builds upon our recent examination of the corresponding state in CHF, where pronounced mode specificity was observed in the dynamics, with predissociation rates larger for levels containing bending excitation. In the present work, a total of 14 S2 state vibrational levels with angular momentum ℓ = 1 were observed for CHCl, and 34 levels for CDCl. The range of ℓ in this case was restricted by the pronounced Renner-Teller effect in the low-lying S1 levels, which severely reduces the fluorescence lifetime for levels with Ka \u3e 0. Nonetheless, by exploiting different intermediate S1 levels, we observed progressions involving all three fundamental vibrations. For levels with long predissociation lifetimes, rotational constants were determined by measuring spectra through different intermediate J levels of the S1 state. Plots of the predissociation linewidth (lifetime) vs. energy for various S2 levels show an abrupt onset, which lies near the calculated threshold for elimination to form C(3P) + HCl on the triplet surface. Our experimental results are compared with a series of high level ab initio calculations, which included the use of a dynamically weighted full-valence CASSCF procedure, focusing maximum weight on the state of interest (the singlet and triplet states were computed separately). This was used as the reference for subsequent Davidson-corrected MRCI(+Q) calculations. These calculations reveal the presence of multiple conical intersections in the singlet manifold

Hydrogen-atom Attack on Phenol and Toluene is \u3cem\u3eortho\u3c/em\u3e-directed

The reaction of H + phenol and H/D + toluene has been studied in a supersonic expansion after electric discharge. The (1 + 1′) resonance-enhanced multiphoton ionization (REMPI) spectra of the reaction products, at m/z = parent + 1, or parent + 2 amu, were measured by scanning the first (resonance) laser. The resulting spectra are highly structured. Ionization energies were measured by scanning the second (ionization) laser, while the first laser was tuned to a specific transition. Theoretical calculations, benchmarked to the well-studied H + benzene → cyclohexadienyl radical reaction, were performed. The spectrum arising from the reaction of H + phenol is attributed solely to the ortho-hydroxy-cyclohexadienyl radical, which was found in two conformers (syn and anti). Similarly, the reaction of H/D + toluene formed solely the ortho isomer. The preference for the ortho isomer at 100–200 K in the molecular beam is attributed to kinetic, not thermodynamic effects, caused by an entrance channel barrier that is ∼5 kJ mol−1 lower for ortho than for other isomers. Based on these results, we predict that the reaction of H + phenol and H + toluene should still favour the ortho isomer under elevated temperature conditions in the early stages of combustion (200–400 °C)

Collisional Excitation of CO by 2.3 eV H Atoms

Vibrational and rotational distributions of CO excited by collisions with 2.3 eV H atoms have been obtained by monitoring the products with vacuum ultraviolet (VUV) laser induced fluorescence. Translational-to-vibrational (T→V) transfer is dominated by the dynamics of collisions occurring in the two wells on the H+CO potential energy surface, one characterizing the HCO radical and the other characterizing COH. The measured vibrational distributions agree well with the results of trajectory calculations performed on the ab initio potential energy surface of Bowman, Bittman, and Harding (BBH). The measured rotational distributions show two significant differences from the calculated ones. First, for v=0 the experiments find more population in Jwells, but inside the van der Waals well. Second, for v=1, the experimental distribution is flat from J=0 to J=10, whereas the calculated one rises from near zero at J=0 to a peak at J=12. This discrepancy appears to be the result of an excessively high ab initio estimate (by a few tenths of an eV) of the barrier for H atoms addition to CO to form COH

A classical trajectory study of the photodissociation of T₁ acetaldehyde: the transition from impulsive to statistical dynamics

Previous experimental and theoretical studies of the radical dissociation channel of T(1) acetaldehyde show conflicting behavior in the HCO and CH(3) product distributions. To resolve these conflicts, a full-dimensional potential-energy surface for the dissociation of CH(3)CHO into HCO and CH(3) fragments over the barrier on the T(1) surface is developed based on RO-CCSD(T)/cc-pVTZ(DZ) ab initio calculations. 20,000 classical trajectories are calculated on this surface at each of five initial excess energies, spanning the excitation energies used in previous experimental studies, and translational, vibrational, and rotational distributions of the radical products are determined. For excess energies near the dissociation threshold, both the HCO and CH(3) products are vibrationally cold; there is a small amount of HCO rotational excitation and little CH(3) rotational excitation, and the reaction energy is partitioned dominantly (>90% at threshold) into relative translational motion. Close to threshold the HCO and CH(3) rotational distributions are symmetrically shaped, resembling a Gaussian function, in agreement with observed experimental HCO rotational distributions. As the excess energy increases the calculated HCO and CH(3) rotational distributions are observed to change from a Gaussian shape at threshold to one more resembling a Boltzmann distribution, a behavior also seen by various experimental groups. Thus the distribution of energy in these rotational degrees of freedom is observed to change from nonstatistical to apparently statistical, as excess energy increases. As the energy above threshold increases all the internal and external degrees of freedom are observed to gain population at a similar rate, broadly consistent with equipartitioning of the available energy at the transition state. These observations generally support the practice of separating the reaction dynamics into two reservoirs: an impulsive reservoir, fed by the exit channel dynamics, and a statistical reservoir, supported by the random distribution of excess energy above the barrier. The HCO rotation, however, is favored by approximately a factor of 3 over the statistical prediction. Thus, at sufficiently high excess energies, although the HCO rotational distribution may be considered statistical, the partitioning of energy into HCO rotation is not.One of the authors D.L.C. acknowledges the financial support of an Australian Postgraduate Research Award. This work has also been supported in large by Grant No. A00104447 from the Australian Research Council and by grants of computer time from the Australian Partnership in Advanced Computing APAC National Merit Allocation Scheme

A tool for helping educators evaluate the level of inquiry in laboratory activities

BACKGROUND Learning science by doing experiments features in the Australian Curriculum: Science as well as university settings. The nature of the experimentation varies immensely, from open-ended to recipe based practical activities. While doing experiments attempts to capture the notion of scientific inquiry, it is a challenge to share understandings of what constitutes inquiry, since there is no universal or concrete definition of science inquiry. Consequently, educators have difficulties understanding how to design, implement and evaluate inquiry-based activities that best engage students and help them learn science. Instead, practitioners tend to create their own working definition of inquiry based on their needs (Buck, Bretz, and Towns, 2008). According to the National Research Council (NRC, 1996), “Scientific inquiry refers to the diverse ways in which scientists study the natural world and propose explanations based on the evidence derived from their work. Inquiry also refers to the activities of students in which they develop knowledge and understanding of scientific ideas, as well as an understanding of how scientists study the natural world.” Based on this articulation and further research, a framework has been developed and trialled by practitioners (National Research Council, 2000; Asay & Orgil, 2010). Using this framework, we have developed a tool that can be used to integrate inquiry in practical activities. This presentation will describe this tool its utility in curriculum. APPROACH The Advancing Science by Enhancing Learning in the Laboratory (ASELL) project has run workshops for over 100 teachers. In the workshops teachers evaluate the level on inquiry of the experiments using the ASELL Inquiry Scaffolding Instrument (AISI) tool based on the framework discussed above. An exemplar inquiry experiment is used to benchmark an open-ended inquiry while most teachers are familiar with recipe experiments. RESULTS Our results show that teachers find the multitude of definitions of inquiry teachers challenging. Further, quite often the definitions are of limited use in the classroom. Despite this confusion, when utilising the AISI, teachers have fairly consistent understandings of inquiry, as shown by statistics. Teachers found the tool useful and would use the tool in their curriculum. Many also said it was a simple tool to use to help them modify their existing experiments and develop them into more inquiry-based experiments. CONCLUSIONS A concerted effort is needed to provide sound and practical tools to help teachers incorporate inquiry in their experiments. The AISI is one such tool that has been found to be useful for increasing the level of inquiry in practical activities.. REFERENCES Asay,L.D.,& Orgill,M.(2010). Analysis of essential features of inquiry found in articles published in The Science Teacher, 1998-2007. Journal of Science Teacher Education, 21, 57-79. Buck,L. B.,Bretz, S. L.,& Towns, M. H.(2008).Characterizing the level of inquiry in the undergraduate laboratory. Journal of College Science Teaching, September/October, 52-58. National Research Council (1996). National science education standards. Washington, DC: National Academy Press. National Research Council (2000). Inquiry and the national science education standards: A guide for teaching and learning. Washington DC: National Academic Press

APCELL: Developing better ways of teaching in the laboratory

The Australian Physical Chemistry Enhanced Laboratory Learning project was established to address deficiencies in Australian physical chemistry laboratory education. The project aims to pool the resources of over 30 universities to develop a protocol for developing and assuring the quality of laboratory teaching experiments. This protocol is based on ‘research-led teaching’ and is underpinned by education research literature. Because of its grounding in research, the project has demonstrated the potential to generate and support further research on teaching and student learning in laboratories. In this paper we describe the progress of the project to date and some of the research methodologies that have been employed

Invigorating science practicals using an inquiry orientated pedagogical tool

BACKGROUND Learning science by ‘doing experiments’ features in the Australian Curriculum: Science as well as university settings. The nature of the experimentation varies immensely, from open-ended to recipe based practical activities. While ‘doing experiments’ attempts to capture the notion of scientific inquiry, it is a challenge to share understandings of what constitutes inquiry, since there is no universal or concrete definition of science inquiry. Consequently, there has been “confusion about what teaching science as inquiry means” (Trowbridge, Bybee and Powell, 2008) and as such teachers may have difficulties understanding how to design, implement and evaluate inquiry-based activities that best engage their students and help them learn scientific concepts. Instead, practitioners tend to create their own working definition of inquiry based on their needs (Buck, Bretz, and Towns, 2008). According to the National Research Council (NRC, 1996), “Scientific inquiry refers to …the activities of students in which they develop knowledge and understanding of scientific ideas, as well as an understanding of how scientists study the natural world.” Based on this articulation and further research, a framework has been developed and trialled by practitioners (National Research Council, 2000; Asay & Orgil, 2010). Using this framework, we have developed a tool that can be used to integrate inquiry into practical activities. This presentation will describe this tool and its utility in curriculum. APPROACH The Advancing Science by Enhancing Learning in the Laboratory (ASELL) project has and continues to run workshops, which engage teachers and students from High Schools across Australia. In the workshops teachers evaluate the level of inquiry of the experiments using the ASELL Inquiry Scaffolding Instrument (AISI) tool based on the framework discussed above. An exemplar inquiry experiment is used to benchmark an open-ended inquiry while most teachers are familiar with recipe experiments. RESULTS Our results show that teachers find the multitude of definitions of inquiry teachers challenging. Further, quite often the definitions are of limited use in the classroom. Despite this confusion, when utilising the AISI, teachers have fairly consistent understandings of inquiry, as shown by statistics. Teachers found the tool useful and would use the tool in their curriculum. Many also said it was a simple tool to use to help them modify their existing experiments and develop them into more inquiry-based experiments. CONCLUSIONS A concerted effort is needed to provide sound and practical tools to help teachers incorporate scientific inquiry in their experiments. The AISI is one such tool that has been found to be useful for increasing the level of inquiry in practical activities. REFERENCES Asay,L.D.,& Orgill,M.(2010). Analysis of essential features of inquiry found in articles published in The Science Teacher, 1998-2007. Journal of Science Teacher Education, 21, 57-79. Buck,L. B.,Bretz, S. L.,& Towns, M. H.(2008).Characterizing the level of inquiry in the undergraduate laboratory. Journal of College Science Teaching, September/October, 52-58. National Research Council (1996). National science education standards. Washington, DC: National Academy Press. National Research Council (2000). Inquiry and the national science education standards: A guide for teaching and learning. Washington DC: National Academic Press.Trowbridge, L.W., Bybee, R.W., & Powell, J.C. (2000). Teaching secondary school science: Strategies for developing scientific literacy. Prentice Hall

ASELL : the advancing science by enhancing learning in the laboratory project

Most science educators and researchers will agree that the laboratory experience ranks as a major factor that influences students’ attitudes to their science courses. Consequently, good laboratory programs should play a major role in influencing student learning and performance. The laboratory program can be pivotal in defining a student\u27s experience in the sciences, and if done poorly, can be a major contributing factor in causing disengagement from the subject area. The challenge remains to provide students with laboratory activities that are relevant, engaging and offer effective learning opportunities