Developing fluency across symbolic-, macroscopic-, and particulate-level representations is central to learning chemistry. Within the chemistry education community, animations and simulations that support multi-representational fluency are considered critical. With advances in the accessibility and sophistication of technology, interactive computer simulations are emerging as uniquely powerful tools to support chemistry learning. In this article, we present examples and resources to support successful implementation of PhET interactive simulations. The PhET Interactive Simulations project at the University of Colorado Boulder has developed over 30 interactive simulations for teaching and learning chemistry. PhET simulations provide dynamic access to multiple representations, make the invisible visible, scaffold inquiry, and allow for safe and quick access to multiple trials, while being engaging and fun for students and teachers. The simulations are readily accessible online, and are designed to be flexible tools to support a wide-range of implementation styles and teaching environments. Here, we introduce the PhET project, including the project’s goals and design principles. We then highlight two simulations for chemistry, Molecule Polarity and Beer’s Law Lab. Finally, we share examples (with resources) of the variety of ways PhET simulations can be used to teach chemistryin lecture, laboratory, and homework.

We simulate and interpret the photodissociation and recombination of I2 - embedded in CO2 clusters using a Hamiltonian that accounts for the strong perturbation of the solute electronic structure by the solvent. The calculated product distributions agree well with the experimental results of Lineberger and co-workers. Excited-state dynamics are more involved than anticipated from the isolated solute potential curves. For example, dissociation does not occur from the A‘ state, and permanent recombination occurs only on the X state, despite the fact that the A state of I2 - is weakly bound. We discuss the role of the cluster environment in bringing about recombination and electronic relaxation in terms of a qualitative model inspired by the theory of electron transfer in solution.

We report product distributions from the photodissociation of I 2 -(OCS) n (n ) 1-26) cluster ions at 790 and 395 nm and discuss implications concerning the structure of these clusters. The experimental results are paralleled by a theoretical investigation of I 2 -(OCS) n structures. The 790 and 395 nm transitions in I 2access dissociative excited states that correlate with the I -+ I( 2 P 3/2 ) and I -+ I*( 2 P 1/2 ) products, respectively. Photoabsorption by I 2 -(OCS) n clusters at 790 nm results in "uncaged" I -(OCS) k and "caged" I 2 -(OCS) k fragments. The 395 nm excitation leads, in general, to three distinct pathways: (1) I 2dissociation on the I -+ I*( 2 P 1/2 ) spin-orbit excited asymptote, competing with the solvent-induced spin-orbit relaxation of I*( 2 P 1/2 ) followed by either (2) I 2dissociation on the I -+ I( 2 P 3/2 ) asymptote or (3) I 2recombination. Pathways 1 and 2 result in a bimodal distribution of the uncaged I -(OCS) k fragments that energetically correlate with the two spin-orbit states of the escaping I atom. The I + Icaging efficiency is determined as a function of the number of solvent OCS molecules at both excitation wavelengths studied. At 790 nm, 100% caging of I 2is achieved for n g 17. For 395 nm excitation, addition of the 17th OCS molecule to I 2 -(OCS) 16 results in a steplike increase in the caging efficiency from 0.25 to 0.68. These results suggest that the first solvent shell around I 2is comprised of 17 OCS molecules. Results of theoretical calculations of the lowestenergy I 2 -(OCS) n cluster structures support this conclusion. The roles of different dominant electrostatic moments of OCS and CO 2 in defining the I 2 -(OCS) n and I 2 -(CO 2 ) n cluster structures are discussed, based on comparison of the photofragment distributions.

The equilibrium structures and the recombination dynamics of I−2 molecular ions embedded in clusters of 3–17 CO2 molecules are studied by Monte Carlo and molecular dynamics simulations. The potential model incorporates, in a self-consistent manner, a description of the I−2 electronic structure that depends on both the I−2 bond length and the solvent degrees of freedom. The influence of the solvent upon the I−2 electronic structure is treated by means of a single effective solvent coordinate, in a manner reminiscent of the theory of electron transfer reactions. This causes the electronic charge to localize on a single I atom when the I–I bond is long or when the solvent cage has become highly asymmetric. The primary focus is the I−2 vibrational relaxation that follows recombination. Simulations of I−2(CO2)16 and I−2(CO2)9 yield vibrational relaxation times of less than 3 ps, even faster than the experimentally observed absorption recovery time of 10–40 ps. It is suggested that the latter time scale is determined by electronic as well as vibrational relaxation mechanisms.