Methyl rotor dependent vibrational interactions in toluene

The methyl rotor dependence of a three state Fermi resonance in S1 toluene at ∼460 cm−1 has been investigated using two-dimensional laser induced fluorescence. An earlier time-resolved study has shown the Fermi resonance levels to have different energy spacings at the two lowest methyl rotor states, m = 0 and 1. The overlapped m = 0 and 1 spectral features have been separated to provide direct spectral evidence for the m dependence of the resonance. The resonance has been probed at m = 3a″1 for the first time and found to be absent, providing further evidence for a large change in the interaction with m. Deperturbing the resonance at m = 0 and 1 reveals that the m dependence arises through differences in the separations of the “zero-order,” locally coupled states. It is shown that this is the result of the local “zero-order” states being perturbed by long-range torsion-vibration coupling that shifts their energy by small amounts. The m dependence of the shifts arises from the Δm = ±3n (n = 1, 2, …) coupling selection rule associated with torsion-rotation coupling in combination with the m2 scaling of the rotor energies, which changes the ΔE for the interaction for each m. There is also an increase in the number of states that can couple to m = 1 compared with m = 0. Consideration of the magnitude of reported torsion-rotation coupling constants suggests that this effect is likely to be pervasive in molecules with methyl rotors

Improved Way to Affix IV Components to Gurneys from Operating Tables

The current issue in the process of transporting a patient from the operating room (OR) to the intensive care unit (ICU) is the risks involved with the IV stand being top-heavy due to two or three IV pumps weighing approximately 15 pounds each. This can lead to injury to the patient, or other personnel, if an instance occurred where the IV stand were to tip over. Having a single person to manage both the IV stand and gurney during transport can increase this risk. To remedy these problems, the project team established the goals of developing a working prototype, testing and evaluating its feasibility, and demonstrating the use of the design to the sponsor. The constraints addressed in completing the design were safety (ex. maintaining access to patient’s head), a quick attach/release function, manufacturability, practicality, cost, and ease of use. The safety of those involved is of utmost importance during this process. To solve these issues two separate solutions were developed in conjunction with two common approaches to affixing IV poles. One solution uses an IV stand on a set wheels and couples this to a bed, while the other transfers individual components to a stand affixed to a bed.https://scholarscompass.vcu.edu/capstone/1139/thumbnail.jp

Preliminary Report on the Behavior of U-Pb Zircon and K-Ar Systems in Polymetamorphosed Ophiolitic Rocks and Batholithic Rocks, Southwestern Sierra Nevada Foothills, California

Ophiolitic rocks of the southwest Sierra Nevada foothills form part of the western metamorphic wall of the Sierra Nevada batholith (fig. 1). Geochronological studies were undertaken to determine: (1) The igneous petrogenetic age of the ophiolite; (2) The age of a prebatholith dynamic greenschist to amphibolite facies metamorphic event experienced by the ophiolite; and (3) The emplacement ages of the batholithic rocks. Geochronological work was interfaced with detailed structural and petrologic studies. A summary of the geochronological data is given in figure 2

Intermolecular vibrations of fluorobenzene-Ar up to 130 cm-1 in the ground electronic state

Sixteen intermolecular vibrational levels of the S0 state of the fluorobenzene-Ar van der Waals complex have been observed using dispersed fluorescence. The levels range up to -130 cm−1 in vibrational energy. The vibrational energies have been modelled using a complete set of harmonic and quartic anharmonic constants and a cubic anharmonic coupling between the stretch and long axis bend overtone that becomes near ubiquitous at higher energies. The constants predict the observed band positions with a root mean square deviation of 0.04 cm−1. The set of vibrational levels predicted by the constants, which includes unobserved bands, has been compared with the predictions of ab initio calculations, which include all vibrational levels up to 70–75 cm−1. There are small differences in energy, particularly above 60 cm−1, however, the main differences are in the assignments and are largely due to the limitations of assigning the ab initio wave-functions to a simple stretch, bend, or combination when the states are mixed by the cubic anharmonic coupling. The availability of these experimental data presents an opportunity to extend ab initio calculations to higher vibrational energies to provide an assessment of the accuracy of the calculated potential surface away from the minimum. The intermolecular modes of the fluorobenzene-Ar2 trimer complex have also been investigated by dispersed fluorescence. The dominant structure is a pair of bands with a -35 cm−1 displacement from the origin band. Based on the set of vibrational modes calculated from the fluorobenzene-Ar frequencies, they are assigned to a Fermi resonance between the symmetric stretch and symmetric short axis bend overtone. The analysis of this resonance provides a measurement of the coupling strength between the stretch and short axis bend overtone in the dimer, an interaction that is not directly observed. The coupling matrix elements determined for the fluorobenzene-Ar stretch-long axis bend overtone and stretch-short axis bend overtone couplings are remarkably similar (3.8 cm−1 cf. 3.2 cm−1). Several weak features seen in the fluorobenzene-Ar2 spectrum have also been assigned

Two dimensional laser induced fluorescence spectroscopy: a powerful technique for elucidating rovibronic structure in electronic transitions of polyatomic molecules

We demonstrate the power of high resolution, two dimensional laser induced fluorescence (2D-LIF) spectroscopy for observing rovibronic transitions of polyatomic molecules. The technique involves scanning a tunable laser over absorption features in the electronic spectrum while monitoring a segment, in our case 100 cm−1 wide, of the dispersed fluorescence spectrum. 2D-LIF images separate features that overlap in the usual laser induced fluorescence spectrum. The technique is illustrated by application to the S1–S0 transition in fluorobenzene. Images of room temperature samples show that overlap of rotational contours by sequence band structure is minimized with 2D-LIF allowing a much larger range of rotational transitions to be observed and high precision rotational constants to be extracted. A significant advantage of 2D-LIF imaging is that the rotational contours separate into their constituent branches and these can be targeted to determine the three rotational constants individually. The rotational constants determined are an order of magnitude more precise than those extracted from the analysis of the rotational contour and we find the previously determined values to be in error by as much as 5%. Comparison with earlier ab initio calculations of the S0 and S1 geometries reveals that the CCSD/6–311G** and RI-CC2/def2-TZVPP levels of theory predict the rotational constants, and hence geometries, with comparable accuracy. Two ground state Fermi resonances were identified by the distinctive patterns that such resonances produce in the images. 2D-LIF imaging is demonstrated to be a sensitive method capable of detecting weak spectral features, particularly those that are otherwise hidden beneath stronger bands. The sensitivity is demonstrated by observation of the three isotopomers of fluorobenzene-d1 in natural abundance in an image taken for a supersonically cooled sample. The ability to separate some of the 13C isotopomers in natural abundance is also demonstrated. The equipment required to perform 2D-LIF imaging with sufficient resolution to resolve the rotational features of large polyatomics is available from commercial suppliers

The toluene-Ar complex: S0 and S1 van der Waals modes, changes to methyl rotation, and torsion-van der Waals vibration coupling

The methyl rotor and van der Waals vibrational levels in the S1 and S0 states of toluene-Ar have been investigated by the technique of two-dimensional laser induced fluorescence (2D-LIF). The S0 van der Waals and methyl rotor levels are reported for the first time, while improved S1 values are presented. The correlations seen in the 2D-LIF images between the S0 and S1 states lead to a reassignment of key features in the S1 ← S0 excitation spectrum. This reassignment reveals that there are significant changes in the methyl rotor levels in the complex compared with those in bare toluene, particularly at low m. The observed rotor energies are explained by the introduction of a three-fold, V3, term in the torsion potential (this term is zero in toluene) and a reduction in the height of the six-fold, V6, barriers in S0 and S1 from their values in bare toluene. The V3 term is larger in magnitude than the V6 term in both S0 and S1. The constants determined are |V3(S1)| = 33.4 ± 1.0 cm−1, |V3(S0)| = 20.0 ± 1.0 cm−1, V6(S1) = −10.7 ± 1.0 cm−1, and V6(S0) = −1.7 ± 1.0 cm−1. The methyl rotor is also found to couple with van der Waals vibration; specifically, the m″ = 2 rotor state couples with the combination level involving one quantum of the long axis bend and m″ = 1. The coupling constant is determined to be 1.9 cm−1, which is small compared with the values typically reported for torsion-vibration coupling involving ring modes

Impact of time to appropriate therapy on mortality in patients with vancomycin-intermediate Staphylococcus aureus infection

Despite the increasing incidence of vancomycin-intermediate Staphylococcus aureus (VISA) infections, few studies have examined the impact of delay in receipt of appropriate antimicrobial therapy on outcomes in VISA patients. We examined the effects of timing of appropriate antimicrobial therapy in a cohort of patients with sterile-site methicillin-resistant S. aureus (MRSA) and VISA infections. In this single-center, retrospective cohort study, we identified all patients with MRSA or VISA sterile-site infections from June 2009 to February 2015. Clinical outcomes were compared according to MRSA/VISA classification, demographics, comorbidities, and antimicrobial treatment. Thirty-day all-cause mortality was modeled with Kaplan-Meier curves. Multivariate logistic regression analysis (MVLRA) was used to determine odds ratios for mortality. We identified 354 patients with MRSA (n = 267) or VISA (n = 87) sterile-site infection. Fifty-five patients (15.5%) were nonsurvivors. Factors associated with mortality in MVLRA included pneumonia, unknown source of infection, acute physiology and chronic health evaluation (APACHE) II score, solid-organ malignancy, and admission from skilled care facilities. Time to appropriate antimicrobial therapy was not significantly associated with outcome. Presence of a VISA infection compared to that of a non-VISA S. aureus infection did not result in excess mortality. Linezolid use was a risk for mortality in patients with APACHE II scores of ≥14. Our results suggest that empirical vancomycin use in patients with VISA infections does not result in excess mortality. Future studies should (i) include larger numbers of patients with VISA infections to confirm the findings presented here and (ii) determine the optimal antibiotic therapy for critically ill patients with MRSA and VISA infections