Molecular Charge-Transfer Cross Sections and Their Correlation with Reactant Ion Structures

Charge-transfer cross sections have been obtained by using time-of-flight techniques, and results correlated with reaction energetics and theoretical structures computed by self-consistent field-molecular orbital methods. Ion recombination energies, structures, heats of formation, reaction energy defects, and 3.0-keV charge-transfer cross sections are presented for reactions of molecular and fragment ions produced by electron bombardment ionization of CH30CH, and CH$l molecules. Relationships between experimental cross sections and reaction energetics involving different ion structures are discussed.

Sensitivity of charge transfer reactions to hydrocarbon ion structures

Charge transfer reactivities of hydrocarbon ions have been measured with time-of-flight techniques, and results correlated with theoretical structures computed by self-consistent field molecular orbital methods. Recombination energies, ion structures, heats of formation, reaction energetics and relative charge transfer cross-sections are presented for molecular and fragment ions produced by electron bombardment ionization of CH4, C2H4, C2H6, C3H8 and C4H10 molecules. Even-electron bridged cations have low ion recombination energies and relatively low charge transfer cross-sections as compared with odd-electron hydrocarbon cations.

The Effect of Grade Point Average on Undergraduates' Understanding of Heat Transfer

Engineering students continue to develop and show misconceptions due to prior knowledge and experiences (Miller, Streveler, Olds, Chi, Nelson, & Geist, 2007). Misconceptions have been documented in students’ understanding of heat transfer(Krause, Decker, Niska, Alford, & Griffin, 2003) by concept inventories (e.g., Jacobi,Martin, Mitchell, & Newell, 2003; Nottis, Prince, Vigeant, Nelson, & Hartsock, 2009). Students’ conceptual understanding has also been shown to vary by grade point average (Nottis et al., 2009). Inquiry-based activities (Nottis, Prince, & Vigeant, 2010) haveshown some success over traditional instructional methods (Tasoglu & Bakac, 2010) in altering misconceptions. The purpose of the current study was to determine whether undergraduate engineering students’ understanding of heat transfer concepts significantly changed after instruction with eight inquiry-based activities (Prince & Felder, 2007) supplementing instruction and whether students’ self reported GPA and prior knowledge, as measured by completion of specific engineering courses, affected these changes. The Heat and Energy Concept Inventory (Prince, Vigeant, & Nottis, 2010) was used to assess conceptual understanding. It was found that conceptual understanding significantly increased from pre- to post-test. It was also found that GPA had an effect on conceptual understanding of heat transfer; significant differences were found in post-test scores onthe concept inventory between GPA groups. However, there were mixed results when courses previously taken were analyzed. Future research should strive to analyze how prior knowledge effects conceptual understanding and aim to reduce the limitations of the current study such as, sampling method and methods of measuring GPA and priorknowledge.

Synthesis Of Triblock Copolymers By Radical Trap Assisted-Atom Transfer Radical Coupling

Monobrominated diblock copolymers composed of poly(styrene) (PSt), poly(methylacrylate) (PMA), or poly(methyl methacrylate) (PMMA) were synthesized by consecutive atom transfer radical polymerizations (ATRP). The brominated diblocks were utilized in atom transfer radical coupling (ATRC) and radical trap-assisted ATRC (RTA-ATRC) reactions to form ABA type triblock copolymers. Once PMMA-PStBr and PSt-PMABrBr were produced by ATRP, the synthes of PSt-PMA-PSt and PMMA-PSt- PMMA by ATRC and also by RTA-ATRC were attempted. The coupling methods were compared and it was found that RTA-ATRC succeeded in synthesizing PSt-PMA-PSt where ATRC could not, and that RTA-ATRC improved coupling over ATRC for PMMAPSt- PMMA. Incorporation of the radical trap 2-methyl-2-nitrosopropane (MNP) midchain allowed for simple thermal cleavage of the triblock to confirm the RTA-ATRC pathway occurred in preference over the head to head radical coupling pathway of ATRC. Triblocks made by ATRC did not cleave under our conditions, as no MNP was present and thus no labile C-O bond was incorporated. The RTA-ATRC pathway allowed for lower catalyst amounts (2 molar equivalents of copper(I)bromide and 2 molar equivalents of copper metal) and a high degree of coupling at lower temperatures (40°C). The RTA-ATRC improved upon ATRC because of its ability to generate a persistent radical and proceed by first order kinetics with respect to the chain end radical.