Search

The Innovative Confinement Concepts Workshop, ICC2002, provided a forum for presentations and exchange of ideas on the science and status of innovative concepts in the U.S. Fusion Energy Program. The workshop, held at the University of Maryland on January 22-24, 2002, included oral presentations addressing the important science and status of the concepts, posters focussed on details of the work, a skunkworks for novel ideas, and breakout sessions preparing for the July 2002 fusion energy Snowmass meeting. This report summarizes the oral presentations. A web site (https:// wormhole.ucllnl.org/ICC2002/) has been established with the abstracts and many of the presentations, both oral and poster, from the workshop.

Infrared spectroscopic studies of weakly bound clusters isolated in solid parahydrogen (pH2) 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)2, HCl–DCl, and (DCl)2 isolated in solid pH2 in the 2.4–4.8 K temperature range. The (HCl)2 spectra show a remarkable amount of fine structures that can be rigorously assigned to vibration–rotation–tunneling transitions of (HCl)2 trapped in double substitution sites in the pH2 matrix where end-over-end rotation of the cluster is quenched. The spectra are assigned using a combination of isotopically (H/D and 35Cl/37Cl) enriched samples, polarized IR absorption measurements, and four-line combination differences. The interchange-tunneling (IT) splitting in the ground vibrational state for in-plane and out-of-plane H35Cl–H37Cl dimers is 6.026(1) and 6.950(1) cm−1, respectively, which are factors of 2.565 and 2.224 smaller than in the gas phase dimer. In contrast, the (DCl)2 results show larger perturbations where the ground vibrational state IT splitting in D35Cl–D37Cl is 1.141(1) cm−1, which is a factor of 5.223 smaller than in the gas phase, and the tunneling motion is quenched in excited intramolecular vibrational states. The results are compared to similar measurements on (HCl)2 made in liquid helium nanodroplets to illustrate the similarities and differences in how both these quantum solvents interact with large amplitude tunneling motions of an embedded chromophore. [ABSTRACT FROM AUTHOR]

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 atoms are produced within solid parahydrogen as the by-products of the 193 nm in situ photolysis of N2O, which induces a two-step tunneling reaction, H + N2O → cis-HNNO → trans-HNNO. The second-order rate constant for the first step to form cis-HNNO is found to be inversely proportional to the N2O concentration after photolysis, indicating that the hydrogen atoms move through solid parahydrogen via quantum diffusion. This reaction only readily occurs at temperatures below 2.8 K, not due to an increased rate constant for the first reaction step at low temperatures but rather due to an increased selectivity to the reaction. The rate constant for the second step of the reaction mechanism involving unimolecular isomerization is shown to be independent of the N2O concentration as expected. The inverse concentration dependence of the rate constant for the reaction step that involves the hydrogen atom demonstrates clearly that quantum diffusion influences the reactivity of the hydrogen atoms in solid parahydrogen, which does not have an analogy in classical reaction kinetics. [ABSTRACT FROM AUTHOR]

We investigated the reaction of methyl formate, HC(O)OCH3, with hydrogen atoms in solid para-hydrogen (p-H2) at 1.74 and 3.3 K with infrared absorption spectroscopy. Hydrogen atoms were produced either upon direct photolysis of HC(O)OCH3 at 193 nm or upon irradiation of Cl2, codeposited with HC(O)OCH3 in p-H2, with light at 365 nm to produce Cl atoms that react with the p-H2 host via the reaction Cl + H2 (ν = 1) → HCl + H induced by subsequent IR irradiation of the p-H2 matrix. We assigned lines at 1785.2, 1170.6, 1104.6, and 879.4/880.5 cm−1 and five additional weak lines to the methoxy carbonyl radical, •C(O)OCH3, and three weak lines at 1751.3, 1152.9, and 994.4/996.8 cm−1 to the formyloxy methyl radical, HC(O)OCH2•, according to the consideration of possible reactions, correlated variations in intensities after each experimental step, and comparison of observed vibrational wavenumbers and IR intensities with values predicted with the B3LYP/aug-cc-pVTZ method. Unlike most reported H-atom diffusion tunneling reactions, the reaction H + HC(O)OCH3 in solid p-H2 at 3.3 K was found to diminish rapidly after IR irradiation, but, similar to reactions of H + N2O and H + HC(O)OH, this reaction was reinitiated when the matrix temperature was decreased from 4.0 K to 1.5 K. We confirmed that the method used to generate the mobile H atoms does not affect the subsequent chemistry. A possible reaction mechanism and the role of this reaction in dark interstellar clouds are discussed. [ABSTRACT FROM AUTHOR]

Multidimensional quantum calculations are conducted on a high-quality ab initio intermolecular potential energy surface to obtain the energies and body-fixed wave functions for the rovibrational states of H2-OH. The degree of body-fixed orientation of OH in some bound states of H2-OH approaches the highest degree of space-fixed orientation.

Rotationally resolved infrared (IR) spectrum of D2-OH in its ground electronic state that are obtained in the OH overtone region at 1.4 Mu(m) via IR - ultraviolet (UV) action spectroscopy are examined. The results are consistent with half-collisions that sample different restricted angular regions of the OH + D2 potential energy surface for each of the initially prepared states.

Issues concerning the photodissociation of OCS in nitrogen and crystalline argon and the investigation of the CO photoproduct by a high-resolution interferometric infrared spectroscope are discussed.

We report FTIR studies of the 193 nm photodecomposition of N-methylformamide (NMF) isolated in solid parahydrogen (pH2) matrices at 1.9 K. By studying the detailed photokinetics we can distinguish between primary and secondary photoproducts. We observe single exponential decay of the NMF precursor upon irradiation and identify three competing primary dissociation channels: HCO + NHCH3; H + CONHCH3; and CO + CH3NH2 with branching ratios of 0.46(7):0.032(8):0.51(6), respectively. Two of the primary photoproducts (NHCH3 and CONHCH3) are observed for the first time using IR spectroscopy and assigned via ab initio calculations of the vibrational frequencies and intensities of these radicals. The dominant radical formation channel HCO + NHCH3 is consistent with efficient C-N peptide bond fission at this wavelength and escape of the nascent radical pair from the pH2 solvent cage. The significant branching 0.51(6) measured for the molecular channel CO + CH3NH2 is unexpected and raises important questions about the details of the in situ photochemistry. Starting from the NMF precursor, we observe and characterize spectroscopically a wide variety of secondary photoproducts including CH2NH, HCN, HNC, HNCO, CH3NCO, CH4, and NH3. [ABSTRACT FROM AUTHOR]

High-resolution infrared spectra of the clusters N2O–(ortho-D2)N and N2O–(HD)N, N=1–4, isolated in bulk solid parahydrogen at liquid helium temperatures are studied in the 2225 cm-1 region of the ν3 antisymmetric stretch of N2O. The clusters form during vapor deposition of separate gas streams of a precooled hydrogen mixture (ortho-D2/para-H2 or HD/para-H2) and N2O onto a BaF2 optical substrate held at ∼2.5 K in a sample-in-vacuum liquid helium cryostat. The cluster spectra reveal the N2O ν3 vibrational frequency shifts to higher energy as a function of N, and the shifts are larger for ortho-D2 compared to HD. These vibrational shifts result from the reduced translational zero-point energy for N2O solvated by the heavier hydrogen isotopomers. These spectra allow the N=0 peak at 2221.634 cm-1, corresponding to the ν3 vibrational frequency of N2O isolated in pure solid parahydrogen, to be assigned. The intensity of the N=0 absorption feature displays a strong temperature dependence, suggesting that significant structural changes occur in the parahydrogen solvation environment of N2O in the 1.8–4.9 K temperature range studied. [ABSTRACT FROM AUTHOR]

Essential to understanding the reaction dynamics of spin-orbit (SO) excited atomic chlorine (2P1/2) with molecular hydrogen is experimental measurements of the SO splitting of Cl in the van der Waals region of the entrance channel to reaction. Here we report high-resolution direct absorption studies of the SO transition (2P1/2←2P3/2) of atomic chlorine isolated in solid molecular hydrogen (H2, HD, and D2). [ABSTRACT FROM AUTHOR]

Essential to understanding the reaction dynamics of spin-orbit (SO) excited atomic chlorine (2P1/2) with molecular hydrogen is experimental measurements of the SO splitting of Cl in the van der Waals region of the entrance channel to reaction. Here we report high-resolution direct absorption studies of the SO transition (2P1/2←2P3/2) of atomic chlorine isolated in solid molecular hydrogen (H2, HD, and D2). [ABSTRACT FROM AUTHOR]

The formation of CH[sub 3]F(ortho-H[sub 2])[sub n] clusters in rapid vapor deposited solid molecular hydrogen containing low concentrations of CH[sub 3]F and ortho-H[sub 2] has been investigated using high-resolution Fourier transform infrared spectroscopy of the C–F stretching mode (ν[sub 3]) of the CH[sub 3]F chromophore. Distributions of CH[sub 3]F(ortho-H[sub 2])[sub n] clusters ranging in size from n=0 to n=12 are synthesized in para-H[sub 2] crystals by systematically varying the ortho-H[sub 2] concentration between 100 to 20 000 parts per million. The rotational motion of CH[sub 3]F is quenched in solid para-H[sub 2]; this simplifies the spectrum such that a single sharp transition is observed for each cluster. In the fundamental ν[sub 3] region, the spectrum consists of a series of well-separated peaks shifted toward lower energy with increasing numbers of nearest neighbor orthohydrogen molecules. The CH[sub 3]F(ortho-H[sub 2])[sub n] clusters are also investigated in the ν[sub 3] overtone region and for analogous transitions of the CD[sub 3]F(ortho-H[sub 2])[sub n]. Theoretical calculations based on an electrostatic interaction potential qualitatively reproduce the measured vibrational and isotopomer dependence of the spectra. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The infrared spectroscopy and rovibrational dynamics of HCl and DCl dopants in solid parahydrogen (pH[sub 2]) were investigated using high-resolution spectroscopic methods. The absorption spectra of HCl and DCl monomers in solid pH[sub 2] closely resemble the corresponding low temperature gas phase spectra, indicating that the gas phase vibrational and rotational quantum numbers of the dopant are conserved within the pH[sub 2] solid. Small deviations from gas phase behavior are observed, however, such as a reduced HCl rotational energy level spacing and splitting of the fivefold orientational degeneracy of HCl rotational states with J=2. In addition, the pure vibrational Q[sub 1](0) (v=1←0, J=0←0) H[sub 2] transition, which is infrared inactive in pure solid pH[sub 2], is detected in the HCl doped sample. We propose that this transition is induced in pH[sub 2] molecules by neighboring HCl molecules through a weak “overlap induction” mechanism that is the only induction mechanism operative for J=0 impurities in pH[sub 2]. Rovibrational transitions are also detected near the induced Q[sub 1](0) H[sub 2] absorption; these are attributed to cooperative transitions involving single photon excitation of pH[sub 2]–HCl pairs. Detailed isotopic analysis reveals that these cooperative transitions involve pure vibrational excitation of the pH[sub 2] and pure rotational excitation of the HCl. Two-molecule transitions have long been studied for isotopic and rotational dopants (e.g., D[sub 2], HD, orthohydrogen) in solid pH[sub 2], but this is the first time such cooperative transitions have been attributed to a chemical impurity in pH[sub 2] matrices. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the reactive quenching of electronically excited OH radicals in collision with molecular hydrogen. Characteristics of the hydrogen atom products; Translational energy distribution of the products; Potential energy surface for hydrogen interacting with OH.

Investigates the state-to-state inelastic scattering event between the hydroxide radical and ortho-hydrogen ion. Evaluation of hydroxide products from vibrational predissociation; Application of ultraviolet probe laser-induced fluorescence; Details on the promotion of hydroxide fragments to the excited spin-orbit state.