The reaction between ground state carbon atoms and propylene, C3H6, was studied at average collision energies of 23.3 and 45.0 kJ mol−1 using the crossed molecular beam technique. Product angular distributions and time-of-flight spectra of C4H5 at m/e=53 were recorded. Forward-convolution fitting of the data yields a maximum energy release as well as angular distributions consistent with the formation of methylpropargyl radicals. Reaction dynamics inferred from the experimental results suggest that the reaction proceeds on the lowest A3 surface via an initial addition of the carbon atom to the π-orbital to form a triplet methylcyclopropylidene collision complex followed by ring opening to triplet 1,2-butadiene. Within 0.3–0.6 ps, 1,2-butadiene decomposes through carbon–hydrogen bond rupture to atomic hydrogen and methylpropargyl radicals. The explicit identification of C4H5 under single collision conditions represents a further example of a carbon–hydrogen exchange in reactions of ground state carbon with unsaturated hydrocarbons. This versatile machine represents an alternative pathway to build up unsaturated hydrocarbon chains in combustion processes, chemical vapor deposition, and in the interstellar medium.

Q ualitative analysis (QA) serves a useful purpose in the general chemistry laboratory curriculum. The groundwork of QA was developed by C. R. Fresenius over 150 years ago. 1 Since then, it has been the basis of experiments that exemplify equilibrium, acidÀbase, redox, and complex formation reactions. However, many of these QA laboratories are "cookbook" in nature; students are presented with a previously derived flowchart to aid in separation and identification of ions. Unfortunately, this requires only minimal thought on the student's part. Perhaps more importantly, without real-world context, the usefulness of this approach is called into question.Attempts to improve upon the traditional method of QA reported in this Journal and others include "n-bottle" experiments using large sets of ions, 2À4 those with smaller sets and an emphasis on periodicity, 5,6 examples using redesigned QA groups to either better suit large classes 7 or to incorporate exam-type questions, 8 experiments involving household chemicals, 9 laboratories involving natural waters, 10,11 and at least one computer simulation. 12 Only one account of a lab requiring students to develop their own separation scheme was found in the literature. 13 This experiment uses a large set of ions and requires nine weeks of lab time. Furthermore, it lacks the contextual setting in which students can frame their learning.A four week QA unit is presented that employs a problembased learning (PBL) module as an alternative to the cookbook experiment. Though rooted in medical education, PBL has also entered into various branches of the chemistry curriculum, as noted by works published in this Journal. For example, PBL has been effectively employed in analytical, 14,15 organic, 16À18 and

The reaction of NO(2) with Fe(2)O(3) has relevance for both atmospheric chemistry and catalysis. Most studies have focused on hematite, α-Fe(2)O(3), as it is the thermodynamic stable state of iron oxide; however, other forms of Fe(2)O(3) naturally occur and may have different chemistries. In this study, we have investigated the reaction products and kinetics for NO(2) reacting with γ-Fe(2)O(3) powder using diffuse reflectance infrared Fourier transform spectroscopy and compared the results to those of previous studies of NO(2) reacting with α-Fe(2)O(3). Both α- and γ-Fe(2)O(3) produce surface-bound nitrate at the pressures examined in this study (24-212 mTorr); surface-bound nitrite products are observed at all pressures for γ-Fe(2)O(3) whereas nitrite was only observed on α-Fe(2)O(3) at lower pressures. Surface-bound NO(+) and Fe-NO products are observed on γ-Fe(2)O(3), which have not been observed with α-Fe(2)O(3). The reaction kinetics show a first-order dependence on NO(2) pressure and this is used to support the hypothesis of unimolecular reaction of adsorbed NO(2) with the γ-Fe(2)O(3) surface as the slow step in the reaction mechanism. The difference in product formation between NO(2) reacting with γ-Fe(2)O(3) and previous studies of α-Fe(2)O(3) illustrate the fact that care must be taken in generalizing reactivity of different polymorphs.

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