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Study designed to determine the relative effectiveness of three different instructional approaches on college chemistry laboratory achievement: the "traditional" approach, the learning cycle approach, and computer simulation.

Matrix infrared spectroscopy has been used to characterize the cocondensation reaction products of H atoms and CS2 in solid argon at 12 K. The major product bands at 1275.2 and 1227.8 cm-l were characterized by photolysis with 320-1000-nm radiation and reappearance on annealing to 18 K to allow diffusion and reaction of trapped H atoms. Deuterium, 13C, and 34S isotopic data were used to identify the major product as the HSCS radical. Vibrational frequencies calculated at the DZP level for the trans conformer are in excellent agreement with the observed spectrum. A most striking feature in the spectrum is the intensification of the 2uc-s mode due to Fermi resonance with the Y~ fundamental. Minor product bands at 1082 and 1059 cm-l increased on 320-1000-nm photolysis, disappeared on 220-1000-nm irradiation, and did not reappear on final sample annealing. DZP calculations support assignment of these bands to cis-and trans-dithioformic acid, respectively.

Nitrogen oxide sulfide species were produced by codeposition of argon/nitric oxide with sulfur species from an argon/sulfur vapor microwave discharge or by deposition of an argon/nitrogen/oxygen/sulfur vapor discharge mixture on a 12 K CsI window. These two new synthetic routes confirmed the identification of the SNO radical and produced the linear SNO + cation and the higher sulfur-containing nitric oxide complex species SSNO at 1772.5 and 670.9 cm -1 . Codeposition of nitric oxide with an argon/nitrogen/sulfur vapor discharge produced a new band at 1815.2 cm -1 , which is assigned to the N-O stretching vibration in the mixed dimer ONNS species. Reaction of superheated sulfur vapor with argon/nitric oxide gave only the 1772.5 and 670.9 cm -1 bands for SSNO with no SNO. In contrast codeposition of Ar/O 2 and Ar/NO produced a trace of NO 2 , but the analogous dioxygen-nitric oxide complex was not observed. Density functional theory was used to calculate structures and frequencies for these product species.

The UV absorption spectrum of trapped s 2 has been studied in N 2 , > ' Ar, Kr and Xe matrices at 4°. and 20°K.• Up.to 26.vibrational bands of the v"=O progression of the 3 !:-+-3 Esystem were observed. In each u u. of the matrices, the origin of the transition was shifted by an amount • characteristic of the particular matrix; red shifts were observed for Xe, Kr and• Ar 1 while N 2 yielded a blue shift.. The vibrational spacing indicated distortion of the potential energy curve under the influence-. of the matrix field. The absorption bands were slightly shaded towards.•. the blue and had a half-width of about 150 em-l ~ At low v' doublet structure was observed • '' '•, ....

Samples formed by codepositing S2 from a superheater source with Ar/O2 on a 10 K substrate exhibit very strong 1403.0-cm-1 and weaker 725.5-cm-1 infrared absorptions. Photolysis decreases these bands slightly and produces SO2 and S2O. The infrared bands show 18O2 and 34S2 shifts appropriate for O−O and S−S fundamental vibrations, and triplet absorptions in mixed isotopic experiments suggesting two equivalent O and two equivalent S atoms in the product complex. Similar results were obtained for Se2 and O2; new absorptions appeared at 1404.5 and 391 cm-1. Ab initio calculations at the SCF, CISD, and CCSD levels of theory failed to find a complex with the observed spectroscopic properties. However, calculations with the BP density functional characterized a singlet (S2)(O2) parallelogram structure bound by 15.6 kJ/mol relative to triplet S2 and O2 with the O−O stretching frequency red-shifted 187 cm-1 and the S−S fundamental blue-shifted 20 cm-1. This weakly bound (S2)(O2) complex is chemically intermediate between the unstable O4 and stable S4 molecules. The argon matrix has made possible the formation of the weak (S2)(O2) complex and DFT with the BP functional has characterized this weak charge-transfer interaction.