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31.
Samartzis PC Lin JJ Ching TT Chaudhuri C Lee YT Lee SH Wodtke AM 《The Journal of chemical physics》2005,123(5):051101
We present results of near-threshold photoionization of N3 photofragments produced by laser photodissociation of ClN3 at 248 nm. The time of flight of recoiling N3 is used to resolve two photochemical channels producing N3, which exhibit different translational energy release. The two forms of N3 resolved in this way exhibit different photoionization thresholds, consistent with their assignment to linear (X 2pi(g)) and cyclic N3. This result agrees with the existing theoretical calculations of excited and ionic states of N3 and strengthens previous experimental results which suggested that the ClN3 photolysis produces a cyclic form of N3. 相似文献
32.
Toledano P Figueiredo Neto AM de Sant'Ana ZA 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(1):486-492
Experimental investigations of lyotropic cholesterics fluids are presented which show that changes in the shape anisotropy and chirality of the micellar population determine the topology of the temperature-concentration phase diagrams. For given amounts of the substances which induce the chirality and modify the shape anisotropy of the micelles, two distinct biaxial cholesteric phases are disclosed in the phase diagrams. This is interpreted in the framework of the catastrophe theory of phase transitions. 相似文献
33.
Measurements of vibrational excitation and deexcitation of NO (v = 2) scattering from a Au(111) surface show that the probability of both processes increases strongly with the kinetic energy of the incident NO. These results are qualitatively consistent with a vibrational energy transfer mechanism involving electron-hole pairs but not with competing adiabatic models. The form of the energy dependence, and other features of the measurements, are not in accord with existing calculations. 相似文献
34.
LaRue JL White JD Nahler NH Liu Z Sun Y Pianetta PA Auerbach DJ Wodtke AM 《The Journal of chemical physics》2008,129(2):024709
Using visible and x-ray photoelectron spectroscopy, we measured the work function of a Au(111) surface at a well-defined submonolayer coverage of Cs. For a Cs coverage producing a photoemission maximum with a He-Ne laser, the work function is 1.61+/-0.08 eV, consistent with previous assumptions used to analyze vibrationally promoted electron emission. A discussion of possible Cs layer structures is also presented. 相似文献
35.
Rahinov I Cooper R Matsiev D Bartels C Auerbach DJ Wodtke AM 《Physical chemistry chemical physics : PCCP》2011,13(28):12680-12692
The Born-Oppenheimer Approximation (BOA) forms the basis for calculating electronically adiabatic potential energy surfaces, thus providing the framework for developing a molecular level understanding of a variety of important chemical problems. For surface chemistry at metal surfaces, it is now clear that for some processes electronically nonadiabatic effects can be important, even dominant; however, the magnitude of BOA breakdown may vary widely from one chemical system to another. In this paper we show that molecular-beam surface scattering experiments can be used to derive quantitative information about the magnitude of BOA breakdown. A state-to-state rate model is used to interpret the pre-exponential factor of the well-known Arrhenius surface temperature dependence of the electronically nonadiabatic vibrational excitation. We also show that reference to a "thermal limit" provides a quick and simple rule of thumb for quantifying BOA breakdown. We demonstrate this approach by comparing electronically nonadiabatic vibrational inelasticity for NO(ν = 0 → 1) to NO(ν = 15 →ν'? 15) and show that the electronically nonadiabatic coupling strengths are of a similar magnitude. We compare experiments for NO and HCl scattering from Au(111) and derive the quantitative relative magnitude for the electronically nonadiabatic influences in each system. The electronically nonadiabatic influences are 300-400 times larger for NO than for HCl, for incidence energies near 0.9 eV. 相似文献
36.
Quinto-Hernandez A Doehla J Huang WT Lien CY Lin WY Lin JJ Wodtke AM 《The journal of physical chemistry. A》2012,116(19):4695-4704
We describe molecular-beam photofragment translational spectroscopy (PTS) experiments using electron impact (EI) ionization product detection to investigate the 193 nm photodissociation of methyl azide (CH(3)N(3)) under collision-free conditions. These experiments are used to derive the branching ratio between channels 1 and 2 [(1) radical channel: CH(3)N(3) + hν (λ = 193 nm) → CH(3) + N(3); (2) molecular channel: CH(3)N(3) + hν (λ = 193 nm) → CH(3)N + N(2)], which have been reported in a previous VUV-photoionization based PTS study. (1) Using electron impact ionization cross sections and ion fragmentation ratios for the various detected products, we derive the branching ratio (X(CH(3)-N(3)))/(X(CH(3)N-N(2))) = (0.017 ± 0.004)/(0.983 ± 0.004). Based on analysis of the kinetic energy release in the radical channel, we find that the cyclic form of N(3) is the dominant product in the radical channel. Only a small fraction of the radical channel produces ground state linear N(3). 相似文献
37.
38.
Bartels N Schäfer T Hühnert J Field RW Wodtke AM 《The Journal of chemical physics》2012,136(21):214201
An intense molecular beam of CO (X(1)Σ(+)) in high vibrational states (v = 17, 18) was produced by a new approach that we call PUMP - PUMP - PERTURB and DUMP. The basic idea is to access high vibrational states of CO e(3)Σ(-) via a two-photon doubly resonant transition that is perturbed by the A(1)Π state. DUMP -ing from this mixed (predominantly triplet) state allows access to high vibrational levels of CO (X(1)Σ(+)). The success of the approach, which avoids the use of vacuum UV radiation in any of the excitation steps, is proven by laser induced fluorescence and resonance enhanced multi-photon ionization spectroscopy. 相似文献
39.
Linsen Zhou Alexander Kandratsenka Charles T. Campbell Alec M. Wodtke Hua Guo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(21):6990-6994
The post‐transition‐state dynamics in CO oxidation on Pt surfaces are investigated using DFT‐based ab initio molecular dynamics simulations. While the initial CO2 formed on a terrace site on Pt(111) desorbs directly, it is temporarily trapped in a chemisorption well on a Pt(332) step site. These two reaction channels thus produce CO2 with hyperthermal and thermal velocities with drastically different angular distributions, in agreement with recent experiments (Nature, 2018 , 558, 280–283). The chemisorbed CO2 is formed by electron transfer from the metal to the adsorbate, resulting in a bent geometry. While chemisorbed CO2 on Pt(111) is unstable, it is stable by 0.2 eV on a Pt(332) step site. This helps explain why newly formed CO2 produced at step sites desorbs with far lower translational energies than those formed at terraces. This work shows that steps and other defects could be potentially important in finding optimal conditions for the chemical activation and dissociation of CO2. 相似文献
40.