Unique Applications of -Hydrogen Matrix Isolation to Spectroscopy and Astrochemistry.

Cryogenic solid -hydrogen (-H) exhibits pronounced quantum effects, enabling unique experiments that are typically not possible in noble-gas matrices. The diminished cage effect facilitates the production of free radicals via photolysis or photoinduced reactions. Electron bombardment during deposition readily produces protonated and hydrogenated species, such as polycyclic aromatic hydrocarbons, that are important in astrochemistry.

Infrared Spectroscopic Studies of Oxygen Atom Quantum Diffusion in Solid Parahydrogen.

The thermally induced diffusion of atomic species in noble gas matrices was studied extensively in the 1990s to investigate low-temperature solid-state reactions and to synthesize reactive intermediates. In contrast, much less is known about the diffusion of atomic species in quantum solids such as solid parahydrogen (p-H). While hydrogen atoms were shown to diffuse in normal-hydrogen solids at 4.

High resolution infrared spectroscopy of (HCl) and (DCl) isolated in solid parahydrogen: Interchange-tunneling in a quantum solid.

Infrared spectroscopic studies of weakly bound clusters isolated in solid parahydrogen (pH) that exhibit large-amplitude tunneling motions are needed to probe how quantum solvation perturbs these types of coherent dynamics. We report high resolution Fourier transform infrared absorption spectra of (HCl), HCl-DCl, and (DCl) isolated in solid pH in the 2.4-4.

Hydrogen atom quantum diffusion in solid parahydrogen: The H + NO → cis-HNNO → trans-HNNO reaction.

The diffusion and reactivity of hydrogen atoms in solid parahydrogen at temperatures between 1.5 K and 4.3 K are investigated by high-resolution infrared spectroscopy.

Hydrogen-atom tunneling reactions with methyl formate in solid para-hydrogen: Infrared spectra of the methoxy carbonyl [•C(O)OCH] and formyloxy methyl [HC(O)OCH•] radicals.

We investigated the reaction of methyl formate, HC(O)OCH, with hydrogen atoms in solid para-hydrogen (p-H) at 1.74 and 3.3 K with infrared absorption spectroscopy.

Solid Parahydrogen Infrared Matrix Isolation and Computational Studies of Li-(CH) Complexes.

Complexes of lithium atoms with ethylene have been identified as potential hydrogen storage materials. As a Li atom approaches an ethylene molecule, two distinct low-lying electronic states are established; one is the A electronic state (for C geometries) that is repulsive but supports a shallow van der Waals well and correlates with the Li 2s atomic state, and the second is a B electronic state that correlates with the Li 2p atomic orbital and is a strongly bound charge-transfer state. Only the B charge-transfer state would be advantageous for hydrogen storage because the strong electric dipole created in the Li-(CH) complex due to charge transfer can bind molecular hydrogen through dipole-induced dipole and dipole-quadrupole electrostatic interactions.

Signatures of a quantum diffusion limited hydrogen atom tunneling reaction.

We are studying the details of hydrogen atom (H atom) quantum diffusion in highly enriched parahydrogen (pH) quantum solids doped with chemical species in an effort to better understand H atom transport and reactivity under these conditions. In this work we present kinetic studies of the 193 nm photo-induced chemistry of methanol (CHOH) isolated in solid pH. Short-term irradiation of CHOH at 1.

Quantum Diffusion-Controlled Chemistry: Reactions of Atomic Hydrogen with Nitric Oxide in Solid Parahydrogen.

Our group has been working to develop parahydrogen (pH2) matrix isolation spectroscopy as a method to study low-temperature condensed-phase reactions of atomic hydrogen with various reaction partners. Guided by the well-defined studies of cold atom chemistry in rare-gas solids, the special properties of quantum hosts such as solid pH2 afford new opportunities to study the analogous chemical reactions under quantum diffusion conditions in hopes of discovering new types of chemical reaction mechanisms. In this study, we present Fourier transform infrared spectroscopic studies of the 193 nm photoinduced chemistry of nitric oxide (NO) isolated in solid pH2 over the 1.

Infrared spectroscopy and 193 nm photochemistry of methylamine isolated in solid parahydrogen.

The in situ UV photolysis of a precursor molecule trapped in a parahydrogen (pH2) matrix is a simple method used to generate isolated radical photofragments that are well suited for infrared spectroscopic studies. However, for molecules that can dissociate via multiple pathways, little is known about how the pH2 matrix influences the branching among these open pathways. We report FTIR spectroscopic studies of the 193 nm photodecomposition of methylamine (MA, CH3NH2) isolated in pH2 quantum matrixes at 1.

Reactions of atomic hydrogen with formic acid and carbon monoxide in solid parahydrogen II: Deuterated reaction studies.

It is difficult to determine whether the measured rate constant for reaction of atomic hydrogen with formic acid reported in Part 1 reflects the H atom quantum diffusion rate or the rate constant for the tunneling reaction step. In Part 2 of this series, we present kinetic studies of the postphotolysis H atom reactions with deuterated formic acid (DCOOD) to address this ambiguity. Short duration 193 nm in situ photolysis of DCOOD trapped in solid parahydrogen results in partial depletion of the DCOOD precursor and photoproduction of primarily CO, CO2, DOCO, HCO and mobile H atoms.

Reactions of atomic hydrogen with formic acid and carbon monoxide in solid parahydrogen I: Anomalous effect of temperature.

Low-temperature condensed phase reactions of atomic hydrogen with closed-shell molecules have been studied in rare gas matrices as a way to generate unstable chemical intermediates and to study tunneling-driven chemistry. Although parahydrogen (pH2) matrix isolation spectroscopy allows these reactions to be studied equally well, little is known about the analogous reactions conducted in a pH2 matrix host. In this study, we present Fourier transform infrared (FTIR) spectroscopic studies of the 193 nm photoinduced chemistry of formic acid (HCOOH) isolated in a pH2 matrix over the 1.

Communication: H-atom reactivity as a function of temperature in solid parahydrogen: The H + N2O reaction.

We present low temperature kinetic measurements for the H + N2O association reaction in solid parahydrogen (pH2) at liquid helium temperatures (1-5 K). We synthesize (15)N2(18)O doped pH2 solids via rapid vapor deposition onto an optical substrate attached to the cold tip of a liquid helium bath cryostat. We then subject the solids to short duration 193 nm irradiations to generate H-atoms produced as byproducts of the in situ N2O photodissociation, and monitor the subsequent reaction kinetics using rapid scan FTIR.

High-resolution infrared spectroscopy of atomic bromine in solid parahydrogen and orthodeuterium.

This work extends our earlier investigation of the near-infrared absorption spectroscopy of atomic bromine (Br) trapped in solid parahydrogen (pH2) and orthodeuterium (oD2) [S. C. Kettwich, L.

Fourier transform infrared studies of ammonia photochemistry in solid parahydrogen.

We present 193 nm in situ photochemical studies of NH3 isolated in solid parahydrogen (pH2) at 1.8 K using Fourier Transform Infrared (FTIR) spectroscopy. By recording FTIR spectra during and after irradiation we are able to identify and assign a number of rovibrational transitions to ortho-NH2(X(2)B1) and NH(X(3)Σ(-)).

Time resolved dynamics of phonons and rotons in solid parahydrogen.

We use femtosecond optical Kerr effect (OKE) spectroscopy to perform time- and wavelength-resolved pump-probe measurements on the energetics and lifetimes of transverse optical phonons and J = 2 rotons in solid para-hydrogen (pH2). By systematically studying the OKE spectroscopy of pH2 in the gas, liquid, and solid phases for delay times up to 300 ps, we can disentangle homodyne and heterodyne contributions in the solid to the signal that results from the slow phonon (900 fs) and fast roton (94 fs) dynamics. In solid pH2 at 8.

Matrix isolation spectroscopy and nuclear spin conversion of NH3 and ND3 in solid parahydrogen.

We present matrix isolation infrared absorption spectra of NH3 and ND3 trapped in solid parahydrogen (pH2) at temperatures around 1.8 K. We used the relatively slow nuclear spin conversion (NSC) of NH3 and ND3 in freshly deposited pH2 samples as a tool to assign the sparse vibration-inversion-rotation (VIR) spectra of NH3 in the regions of the ν2, ν4, 2ν4, ν1, and ν3 bands and ND3 in the regions of the ν2, ν4, ν1, and ν3 fundamentals.

Photodissociation of N-methylformamide isolated in solid parahydrogen.

We report FTIR studies of the 193 nm photodecomposition of N-methylformamide (NMF) isolated in solid parahydrogen (pH(2)) matrices at 1.9 K. By studying the detailed photokinetics we can distinguish between primary and secondary photoproducts.

Does obesity affect outcomes of treatment for lumbar stenosis and degenerative spondylolisthesis? Analysis of the Spine Patient Outcomes Research Trial (SPORT).

Study Design: Retrospective subgroup analysis of prospectively collected data according to treatment received.

Objective: The purpose of this study was to determine whether obesity affects treatment outcomes for lumbar stenosis (SpS) and degenerative spondylolisthesis (DS).

Summary Of Background Data: Obesity is thought to be associated with increased complications and potentially less favorable outcomes after the treatment of degenerative conditions of the lumbar spine.

Transient H2O Infrared Satellite Peaks Produced in UV Irradiated Formic Acid Doped Solid Parahydrogen.

We report newly identified satellite features of the R(0) rovibrational transition of all the fundamental modes of HDO and the ν3 mode of H2O measured via FTIR spectroscopy immediately after the 193 nm in situ photolysis of formic acid (HCOOH and DCOOD) in solid parahydrogen. The intensities of these satellite features decay slowly with a time constant of τ = 121(7) min after photolysis, even when the sample is maintained below 2 K. We propose that the van der Waals complex H···H2O (H···HDO) is the carrier of the satellite peaks and that these metastable complexes are produced after the low-temperature tunneling reaction of the OH (OD) photoproduct with the parahydrogen host.

Infrared spectroscopy of the amide I mode of N-methylacetamide in solid hydrogen at 2-4 K.

We report high-resolution (0.05 cm(-1)) FTIR spectra of the fundamental and first overtone of the amide I mode of trans-N-methylacetamide (NMA) trapped in solid molecular hydrogen (SMH) at cryogenic temperatures with low (0.03%) and high (55%) ortho-hydrogen (oH(2)) concentrations.

Conformation resolved induced infrared activity: trans- and cis-formic acid isolated in solid molecular hydrogen.

We report combined experimental and theoretical studies of infrared absorptions induced in solid molecular hydrogen by different conformers of formic acid (HCOOH, FA). FTIR spectra recorded in the H(2) fundamental region (4120-4160 cm(-1)) reveal a number of relatively strong trans-FA induced Q-branch absorptions that are assigned by studying both FA-doped parahydrogen (pH(2)) and normal hydrogen (nH(2)) samples. The induced H(2) absorptions are also studied for HCOOD doped nH(2) crystals for both the trans and cis conformers that show resolvable differences.

Theoretical Study of Vibrationally Averaged Dipole Moments for the Ground and Excited C═O Stretching States of trans-Formic Acid.

Recent experimental studies of trans-formic acid (FA) in solid para-hydrogen (pH2) highlighted the importance of vibrationally averaged dipole moments for the interpretation of the high-resolution infrared (IR) spectra, in particular for the C═O stretch (ν3) mode. In this report, dipole moments for the ν3 ground (v = 0) and excited (v = 1, 2, 3, and 4) anharmonic vibrational states in trans-FA are investigated using two different approaches: a single mode approximation, where the vibrational states are obtained from the solution of the one-dimensional Schrödinger equation for the harmonic normal coordinate, and a limited vibrational configuration interaction (VCI) approximation. Density functional theory (B3LYP, BPW91) and correlated ab initio (MP2 and CCSD(T)) electronic methods were employed with a number of double- and triple-ζ and correlation consistent basis sets.

Cervical spine injuries in American football.

American football is a high-energy contact sport that places players at risk for cervical spine injuries with potential neurological deficits. Advances in tackling and blocking techniques, rules of the game and medical care of the athlete have been made throughout the past few decades to minimize the risk of cervical injury and improve the management of injuries that do occur. Nonetheless, cervical spine injuries remain a serious concern in the game of American football.

Solvent dependence of the N-methylacetamide structure and force field.

The N-methylacetamide molecule (NMA) is an important model for peptide and protein vibrational spectroscopy as it contains the main amide chromophore. In the past, some observed NMA geometry and spectral features could not be entirely explained at the harmonic level or by a single-conformer model. In particular, the spectra were found to be very dependent on molecular environment.

Emergency evaluation, imaging, and classification of thoracolumbar injuries.

Thoracolumbar injuries usually are the result of high-energy trauma and frequently are associated with multisystem concomitant injuries. Whenever a thoracolumbar injury is suspected, a prompt and thorough evaluation should be performed in the emergency department, using the guidelines of the American College of Surgeons and including full primary and secondary surveys as well as resuscitation. Protection of the spine and spinal cord is of paramount importance during the initial evaluation.