Spectroscopy of 1,4,4-trifluorocyclobutene

A new compound, 1,4,4-trifluorocyclobutene (144FCB), has been obtained as a byproduct in the reduction of perfluorocyclobutene with sodium borohydride. A comprehensive spectroscopic study of 144FCB has been undertaken including microwave, IR, Raman and NMR data. Ground state rotational constants, A=3629.34, B=2600.74, and C=2098.93 MHz, were derived from the microwave data and used to distinguish 144FCB from other possible isomers and to propose a structure. NMR chemical shifts and coupling constants and the vibrational fundamentals are assigned and compared to other members of the cyclobutene family. Frequencies of vibrational fundamentals of 144FCB (cm-1) are: (a') 3126, 2967, 1679, 1457, 1377, 1245, 1179, 1045, 914, 752, 690, 577, 453, 263, 213; (a") 3000, 1198, 1061, 938, 821, 577, 381, 190, -. A small amount of 3,3,4-trifluorocyclobutene has also been found in the products of the reduction reaction, and its NMR spectra and its IR spectrum are reported.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28527/1/0000324.pd

An ensemble of structures of Burkholderia pseudomallei 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase

An ensemble of crystal structures are reported for 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase from B. pseudomallei. The structures include two vanadate complexes, revealing the structure of a close analogue of the transition state for phosphate transfer

Photo-Hall studies of compound semiconductors

The III-V compound semiconductor materials are used in a wide variety of electronic, optoelectronic and microwave device applications. Temperature dependent photo-Hall effect measurements have been made on the high purity compound semiconductors GaAs, InP and a ternary alloy In\sb{0.53}Ga\sb{0.47}As. The major emphasis of this work involves the phenomenon of persistent photoconductivity. This phenomenon has been used to facilitate the electrical characterization of homogeneous and inhomogeneous thin epitaxial semiconductor layers. This effect is associated with a reduction in the surface and substrate interface depletion that occurs upon illumination of the sample with above band gap light at cryogenic temperatures. After illumination, the effects of a photoinduced charge neutral region persists, until at higher temperatures, the sample relaxes back to its original state. For homogeneous layers, the mobility, which is a measure of the microscopic quality of the crystal, remains unchanged after illumination. The persistent photoeffect strictly results from the increase in the effective electrical thickness of the layer. By utilizing the persistent photoeffect, electrical measurements have been made on thin high purity GaAs, which was semi-insulating in the dark because of surface and interface depletion.The effects of illumination of inhomogeneous materials has also been studied. Hall measurements on inhomogeneous GaAs and InP layers in the dark show no unusual features. When these layers are illuminated with above band gap light at low temperatures, anomalous values for the mobility and carrier concentration have been measured. In one metalorganic chemical vapor deposition (MOCVD) grown GaAs sample, the low temperature mobility was decreased by two orders of magnitude after illumination. These particular results have their origin in the occurrence of an accumulation of impurities at the epilayer-substrate interface. The presence of this doping spike is not detected when electrical measurements are made in the dark because of the interface depletion.These results clearly show that the persistent photo-Hall (i.e., Hall data taken with momentary illumination of the sample with above band gap light at low temperatures) is a powerful method for looking at the electrical properties of thin high purity semiconductors.U of I OnlyETDs are only available to UIUC Users without author permissio

Growth of a crystalline and ultrathin MgO film on Fe(001)

The narrow temperature-window for obtaining a crystalline MgO film on Fe(001) has been found using in-situ STM. When Mg was deposited on Fe(001) at RT, post-oxidized at 300 °C, and additionally annealed at 400 °C, an ultrathin and crystalline MgO film was formed. It has been concluded that, in order to grow a high-quality and crystalline MgO film on Fe(001), it requires two steps, i.e., Mg film formation on the substrate at RT and subsequent annealing at the proper substrate temperature under O2 exposure for Mg atoms to be oxidized and crystallized at their deposited sites without being agglomerated

VIBRATIONAL SPECTRA AND ASSIGNMENT FOR 3,3,4,4-TETRAFLUOROCYCLOBUTENE-D0D_{0}-D1D_{1}, AND −D2-D_{2}

1. A. E. Andrews, S. L. Maruca, K. W. Hillig II, R. L. Kuczkowski, and N. C. Craig, J. Phys. Chem. 95, 7714 (1991).Author Institution: Department of Chemistry, Oberlin CollegeThe three hydrogen-deuterium isotopomers of tetrafluorocyclobutene are near-prolate symmetric tops. The two $C_{2{v}}$ species are unusual in having their dipole axes perpendicular to the pseudo-figure axis, $I_{a}$. In addition, the $I_{a}$ axis is parallel to the dipole axis in the $d_{0}$ species but perpendicular to it in the $d_{2}$ species. 1 Under these circumstances B-type and C-type band shapes are essentially indistinguishable in gas-phase infrared spectra. Nonetheless, a reasonably complete and convincing assignment of vibrational fundamentals can be made from the infrared and Raman spectra of the three isotopomers, considered together. For the $d_{0}$ species selection rules and fundamentals (in $cm^{-1}$) are ($a_{1}$; IR, C-type; R, pol) 3154, 1564, 1350, 1155, 1025, 755, 500, 277; ($a_{2}$; IR, -; R, dp) --, 966, 348, --, 132; ($b_{1}$ IR, A-type; R, dp) 3108, 1338, 1177, 1058, 730, 614, 431; ($b_{2}$ IR, B-type; R, dp) 1340, 799, 366, 208