Jack Barbera

Femtosecond dynamics of Cu(H2O)2

The ultrafast relaxation dynamics of Cu(H(2)O)(2) is investigated using femtosecond photodetachment-photoionization spectroscopy. In addition, stationary points on the Cu(H(2)O)(2) anion, neutral, and cation potential energy surfaces are characterized by ab initio electronic structure calculations. Electron photodetachment from Cu(-)(H(2)O)(2) initiates the dynamics on the ground-state potential energy surface of neutral Cu(H(2)O)(2). The resulting Cu(H(2)O)(2) complexes experience large-amplitude H(2)O reorientation and dissociation. The time evolution of the Cu(H(2)O)(2) fragmentation products is monitored by time-resolved resonant multiphoton ionization. The parent ion, Cu(+)(H(2)O)(2), is not detected above background levels. The rise to a maximum of the Cu(+) signal from Cu(-)(H(2)O)(2), and the decay of the Cu(+)(H(2)O) signal from Cu(-)(H(2)O)(2) have similar tau approximately 10 ps time dependences to the corresponding signals from Cu(-)(H(2)O), but display clear differences at very short and long times. The experimental observations can be understood in terms of the following picture. Prompt dissociation of H(2)O from nascent Cu(H(2)O)(2) gives rise to a vibrationally excited Cu(H(2)O) complex, which dissociates to Cu+H(2)O due to coupling of H(2)O internal rotation to the dissociation coordinate. This prompt dissociation removes all intra-H(2)O vibrational excitation from the intermediate Cu(H(2)O) fragment, which quenches the long time vibrational predissociation to Cu+H(2)O previously observed in analogous experiments on Cu(-)(H(2)O).

Connecting achievement motivation to performance in general chemistry

Student success in chemistry is inherently tied to motivational and other affective processes. We investigated three distinct constructs tied to motivation: self-efficacy, interest, and effort beliefs. These variables were measured twice over the course of a semester in three sections of a first-semester general chemistry course (n = 170). We explored the connections that exist among these three constructs as well as their connections to course performance. Multiple regression and path analysis revealed that self-efficacy measured during week 12 was the strongest predictor of final course grade followed by situational interest. We also report that personal interest is a significant predictor of future self-efficacy. Our results add to the growing literature on psychological constructs within chemistry education by identifying variables related to motivation that have a significant connection to course performance among chemistry students. We briefly address how these variables could be targeted in the classroom.

Development and evaluation of a chemistry-specific version of the academic motivation scale (AMS-Chemistry)

Fundamentally concerned with motivation, self-determination theory (SDT) represents a framework of several mini-theories to explore how social context interacts with peoples motivational types categorized by degree of regulation internalization. This paper aims to modify an existing theory-based instrument (Academic Motivation Scale, or AMS) and provide validity evidence for the modified instrument (Academic Motivation Scale-Chemistry) as a measure of seven types of student motivation toward chemistry. The paper explores how motivation as measured by AMS-Chemistry is related to student academic achievement and attendance. In a pilot study, the unmodified AMS showed good reliability, reasonable data fit, and the ability to detect motivational differences by sex in college chemistry courses. Based on the pilot study results, expert panel discussions, and cognitive interviews with students, the Academic Motivation Scale – Chemistry (AMS-Chemistry) was developed. AMS-Chemistry was administered to university students in a first semester general chemistry course twice within a semester. An examination of validity evidence suggested that the AMS-Chemistry data could be used to investigate student motivation toward chemistry. Results showed students were extrinsically motivated toward chemistry on average, and there was an overall motivational difference favoring males with a medium effect size. Correlation studies showed motivation was not associated with academic achievement at the beginning of the term, but intrinsic motivation subscales (to know, to experience, and to accomplish) were positively associated with academic achievement at the end of the term. Results also showed that students who persisted in class attendance scored higher on intrinsic motivation subscales than those who did not persist. The 28-item AMS-Chemistry is easy to administer and can be used to better understand students’ motivation status and how it might change across the curriculum. Faculty interested in promoting student intrinsic motivation may also use the AMS-Chemistry to evaluate the impact of their efforts.

Femtosecond dynamics of Cu(CD3OD).

We report the femtosecond nuclear dynamics of Cu(CD3OD) van der Waals clusters, investigated using photodetachment-photoionization spectroscopy. Photodetachment of an electron from Cu-(CD3OD) with a 150 fs, 398 nm laser pulse produces a vibrationally excited neutral complex that undergoes ligand reorientation and dissociation. The dynamics of Cu(CD3OD) on the neutral surface is interrogated by delayed femtosecond resonant two-photon ionization. Analysis of the resulting time-dependent signals indicates that the nascent Cu(CD3OD) complex dissociates on two distinct time scales of 3 and 30 ps. To understand the origins of the observed time scales, complimentary studies were performed. These included measurement of the photoelectron spectrum of Cu-(CD3OD) as well as a series of calculations of the structure and the electronic and vibrational energies of the anion and neutral complexes. Based on the comparisons of the experimental and calculated results for Cu(CD3OD) with those obtained from earlier studies of Cu(H2O), we conclude that the 3 ps time scale reflects the energy transfer from the rotation of CD3OD in the complex to the dissociation coordinate, while the 30 ps time scale reflects the energy transfer from the excited methyl torsion states to the dissociation coordinate.

Chemistry vs. Physics: A Comparison of How Biology Majors View Each Discipline

A student’s beliefs about science and learning science may be more or less sophisticated depending on the specific science discipline. In this study, we used the physics and chemistry versions of the Colorado Learning Attitudes about Science Survey (CLASS) to measure student beliefs in the large, introductory physics and chemistry courses, respectively. We compare how biology majors — generally required to take both of the courses — view these two disciplines. We find that these students’ beliefs are more sophisticated about physics (more like the experts in that discipline) than they are about chemistry. At the start of the term, the average % Overall Favorable score on the CLASS is 59% in physics and 53% in chemistry. The students’ responses are statistically more expert‐like in physics than in chemistry on 10 statements (P ⩽ 0.01), indicating that these students think chemistry is more about memorizing disconnected pieces of information and sample problems, and has less to do with the real world. In ad...

Evaluation of the influence of wording changes and course type on motivation instrument functioning in chemistry

Increased understanding of the importance of the affective domain in chemistry education research has led to the development and adaptation of instruments to measure chemistry-specific affective traits, including motivation. Many of these instruments are adapted from other fields by using the word ‘chemistry’ in place of other disciplines or more general ‘science’ wording. Psychometric evidence is then provided for the functioning of the new adapted instrument. When an instrument is adapted from general language to specific (e.g. replacing ‘science’ with ‘chemistry’), an opportunity exists to compare the functioning of the original instrument in the same context as the adapted instrument. This information is important for understanding which types of modifications may have small or large impacts on instrument functioning and in which contexts these modifications may have more or less influence. In this study, data were collected from the online administration of scales from two science motivation instruments in chemistry courses for science majors and for non-science majors. Participants in each course were randomly assigned to view either the science version or chemistry version of the items. Response patterns indicated that students respond differently to different wordings of the items, with generally more favorable response to the science wording of items. Confirmatory factor analysis was used to investigate the internal structure of each instrument, however acceptable data-model fit was not obtained under any administration conditions. Additionally, no discernable pattern could be detected regarding the conditions showing better data-model fit. These results suggest that even seemingly small changes to item wording and administration context can affect instrument functioning, especially if the change in wording affects the construct measured by the instrument. This research further supports the need to provide psychometric evidence of instrument functioning each time an instrument is used and before any comparisons are made of responses to different versions of the instrument.

Ultrafast Photoelectron Spectroscopy of Transient Species

Ultrafast pump-probe studies of recombination photodissociated, size-selected dihalide cluster anions show long time coherent motions and the resulting non-statistical energy flow in the cluster. Transient photoelectron spectroscopy uniquely identifies the products and their internal energy.