The UV absorption spectrum of C60 (buckminsterfullerene): A narrow band at 3860 Å

The absorption spectrum of the special C60 cluster buckminsterfullerene has been studied in a supersonic beam by laser depletion of the cold van der Waals complexes of C60 with benzene and methylene chloride. Both complexes were found to display a single, isolated absorption band in the near ultraviolet superimposed on a structureless absorption continuum. For the methylene chloride complex this feature is centered at 3860 Å, and is roughly 50 cm−1 wide. In the benzene van der Waals cluster, the corresponding feature is located at 3863 Å, and has a similar width. This spectrum is tentatively assigned to the 0–0 band of the lowest 1T1u<--1Ag (LUMO+1<--HOMO) transition of a truncated icosahedral carbon shell structure, broadened by coupling to the underlying quasicontinuum of ground state vibrational levels

Photophysics of buckminsterfullerene and other carbon cluster ions

The laser-induced fragmentation behavior of positive carbon cluster ions has been investigated by tandem time-of-flight techniques for the jet-cooled clusters up to 80 atoms in size. Two distinct photophysical regimes were found. The first applies to clusters with 34 atoms or more, all of which dissociate to produce even numbered fragments. Large even clusters fragment by the loss of the high energy species C2, odd ones lose a C atom. The second regime applies to clusters composed of 31 or less atoms, all of which fragment by the loss of C3. These two regimes are sharply separated by C + 32 which fragments to produce small cluster ions in the 10–19 atom size range. Fragmentation of the large clusters occurs on a microsecond or faster time scale only at very high levels of excitation (>12.8 eV). These photophysical results are interpreted as consequences of the large even clusters having edgeless, spheroidal cage structures while the small ones have linear chain or ring structures

Reality check: Asynchronous instruction works!

Never before had I asked a student to cite an emoticon. In traditional classroom instruction, it is unlikely that this would have come up at all. However, in an asynchronous course, you never know where an online threaded discussion on citation formats will lead. As library educators, we have the opportunity to have an impact on a student\u27s chances for success in locating and managing information. We must draw upon the students\u27 familiarity with new technologies and teach them how to effectively articulate their information need, identify appropriate resources, evaluate what has been retrieved, and redirect their continued searching. The challenge that confronts us is compounded by the fact that many students enter the library only through a virtual door. In recognition of the shifting paradigm involving information and new technologies, Purdue University\u27s Electrical Engineering Technology (EET) program asked the Purdue Libraries to develop a credit course that would teach the students how to effectively locate, evaluate, and present information. The course, Information Strategies, has been a required course in EET was designed and taught by the libraries\u27 faculty since 1993. It has subsequently been adapted to other disciplines, as well. As evolution of new technologies continued, course instructors proposed the development of an asynchronous version of this course to the Indiana Higher Education Telecommunications System (IHETS). The development grant was awarded and the first Web-based version of this course was offered Spring 1999. The purpose of the IHETS course development grant was to enhance and convert [the Information Strategies course] to a digital format, which will allow asynchronous statewide access. In July 1998, the investigators, Professors Sheila Curl, Leslie Reynolds, Brent Mai, and Alexius Smith, began adapting the traditional course for delivery over the Internet

Measurement of Urinary Pesticide Biomarkers Among Latina Farmworkers in Southwestern Idaho

Background Women who work in agriculture may have greater risk of pesticide exposure than men who share this occupation. Despite an increase in the fraction of the agricultural workforce comprised by women, few studies have characterized pesticide exposure in the USA with a focus on among these workers. Objective This pilot study aimed to describe pesticide exposure in a cohort of Latina farmworkers in farming communities in southwestern Idaho. Methods We collected urine samples from 29 Latina farmworkers, which were analyzed for 11 pesticide biomarkers. We evaluated the effect of pesticide spray season on urinary biomarker levels, and explored the effect of self-reported status as a pesticide handler on measured exposures. Results No significant differences were found between biomarker levels in samples collected during the nonspray and spray seasons. We observed 11 extreme outlying values in samples collected during the pesticide spray season. The most extreme outlying values (MDA: 51.7 ng/mL; 3-PBA: 11.8 ng/mL; trans-DCCA: 23.4 ng/mL; and 2,4-D: 31.1 ng/mL) were all provided during the spray season by women who reported loading, mixing or applying pesticides. Conclusions These results provide suggestive evidence that Latina farmworkers who handle pesticides during the spray season may be at an increased risk of exposure to organophosphate and pyrethroid insecticides, as well as the herbicide 2,4- D. We recommend that future research into pesticide exposures among farmworkers should include particular focus on this group

Magnetic Properties of Undoped C60C_{60}

The Heisenberg antiferromagnet, which arises from the large $U$ Hubbard model, is investigated on the $C_{60}$ molecule and other fullerenes. The connectivity of $C_{60}$ leads to an exotic classical ground state with nontrivial topology. We argue that there is no phase transition in the Hubbard model as a function of $U/t$, and thus the large $U$ solution is relevant for the physical case of intermediate coupling. The system undergoes a first order metamagnetic phase transition. We also consider the S=1/2 case using perturbation theory. Experimental tests are suggested.Comment: 12 pages, 3 figures (included

Semiconductor cluster beams: One and two color ionization studies of Six and Gex

Supersonic beams of clusters of Si and Ge atoms have been produced by laser vaporization followed by supersonic expansion in a helium carrier. The cluster beams were characterized by F2(7.9 eV) and ArF(6.4 eV) excimer laser ionization accompanied by time-of-flight mass analysis. In addition, the feasibility of a resonant two-photon ionization (R2PI) spectroscopic study was explored by two-color experiments involving initial excitation with the second (2.36 eV) and third (3.54 eV) harmonics of the Nd:YAG followed by excimer laser ionization. All two-photon ionization processes were found to produce extensive fragmentation of the larger clusters. The observed fragmentation pattern for the silicon and germanium clusters were remarkably similar to each other, but drastically different from that seen for metal clusters in the same apparatus. Unlike metal clusters, which tend to lose one atom at a time, these semiconductor clusters appear to fragment by a fission process, the daughter ions falling almost exclusively in the size range from 6 to 11 atoms. Time delay studies in the two-color experiments established that clusters of both Si and Ge have excited electronic states with lifetimes of approximately 100 ns. This again is dramatically different from the behavior found with metal clusters, and indicates the feasibility of R2PI spectroscopy on these cold semiconductor particles. The existence of such long-lived excited states indicates that there is probably an energy gap between the band of electronic states being excited and the ground electronic state