Search results for "PHOTODISSOCIATION"

Multiphoton Absorption of Myoglobin Nitric-Oxide complex: Relaxation by D-NEMD of a Stationary State

2012

ABSTRACT: The photodissociation and geminate recombination of nitric oxide in myoglobin, under continuous illumination, is modeled computationally. The relaxation of the photon energy into the protein matrix is also considered in a single simulation scheme that mimics a complete experimental setup. The dynamic approach to non-equilibrium molecular dynamics is used, starting from a steady state, to compute its relaxation to equilibrium. Simulations are conducted for the native form of sperm whale myoglobin and for two other mutants, V68W and L29F, illustrating a fair diversity of spatial and temporal geminate recombination processes. Energy flow to the heme and immediate protein environment …

Pulsed photodissociation in an ion cyclotron resonance trap: extending the time range for unimolecular dissociation studies of metal clusters

1997

Heterocyclic photorearrangements. Photoinduced rearrangements of 1,2,4-oxadiazoles substituted by an XYZ side chain sequence

1988

Photoinduced rearrangements of 1,2,4-oxadiazoles substituted by an XYZ side chain sequence at position 3 of the ring have been recognized. Examples taken out from previous results have been emphasized and some other patterns dealing with a 3-phenoxy and 3-enaminoketone sequence have been investigated. An intermediate species derived from photolysis of the ring O-N bond and characterized by a continuous 6π electron system involving the side chain sequence, was suggested to give ring closure to the rearrangement product.

Iodine and mercury resonance lamps for kinetics experiments and their spectra in the far ultraviolet

2000

Electrodeless iodine and mercury iodide radio-frequency discharge lamps have been made to provide intense sources of resonance radiation of iodine and mercury in the 183-253 nm region. Production technology and emission spectra in the ultraviolet and vacuum ultraviolet regions are described. Both lamps (iodine and mercury iodide) are designed and used for monitoring the iodine 2P1/2 (206.163 nm) and 2P3/2 (183.038 nm) level population kinetics after flash photolysis of I2 or other precursor molecules in laboratory experiments. The technique is suitable for the investigation of the gas phase reaction kinetics following the photolysis of I2 in the presence of O3.

A machine learning examination of hydroxyl radical differences among model simulations for CCMI-1

2020

The hydroxyl radical (OH) plays critical roles within the troposphere, such as determining the lifetime of methane (CH4), yet is challenging to model due to its fast cycling and dependence on a multitude of sources and sinks. As a result, the reasons for variations in OH and the resulting methane lifetime (τCH4), both between models and in time, are difficult to diagnose. We apply a neural network (NN) approach to address this issue within a group of models that participated in the Chemistry-Climate Model Initiative (CCMI). Analysis of the historical specified dynamics simulations performed for CCMI indicates that the primary drivers of τCH4 differences among 10 models are the flux of UV li…

In situ measurements of molecular iodine in the marine boundary layer: the link to macroalgae and the implications for O<sub>3</…

2010

Abstract. Discrete in situ atmospheric measurements of molecular iodine (I2) were carried out at Mace Head and Mweenish Bay on the west coast of Ireland using diffusion denuders in combination with a gas chromatography-mass spectrometry (GC-MS) method. I2, IO and OIO were also measured by long-path differential optical absorption spectroscopy (LP-DOAS). The simultaneous denuder and LP-DOAS I2 measurements were well correlated (R2=0.80) but the denuder method recorded much higher concentrations. This can be attributed to the fact that the in situ measurements were made near to macroalgal sources of I2 in the intertidal zone, whereas the LP-DOAS technique provides distance-averaged mixing rat…

Raman spectroscopy and crystal-field split rotational states of photoproducts CO and H2 after dissociation of formaldehyde in solid argon.

2012

Raman signal is monitored after 248 nm photodissociation of formaldehyde in solid Ar at temperatures of 9-30 K. Rotational transitions J = 2 ← 0 for para-H(2) fragments and J = 3 ← 1 for ortho-H(2) are observed as sharp peaks at 347.2 cm(-1) and 578.3 cm(-1), respectively, which both are accompanied by a broader shoulder band that shows a split structure. The rovibrational spectrum of CO fragments has transitions at 2136.5 cm(-1), 2138.3 cm(-1), 2139.9 cm(-1), and 2149 cm(-1). To explain the observations, we performed adiabatic rotational potential calculations to simulate the Raman spectrum. The simulations indicate that the splitting of rotational transitions is a site effect, where H(2) …

Anomalous binding sequence of CO ligands to an anionic triplatinum carbonyl complex

2005

Abstract A systematic density functional theory study on the structures and binding energies of triplatinum carbonyls Pt 3 ( CO ) x q , with x  = 1–6 and q  = 0, −1, reveals an anomalous trend in binding energies of the CO ligands to the triangular platinum core, with the first three ligands strongly bound at terminal Pt sites, followed by weaker bound ligands at Pt–Pt bridge sites for x  = 4–6. This work provides a novel explanation to the anomalous CO binding trend reported in mid-1990s from collision-induced dissociation and photodissociation experiments.

Dissociative charge transfer from highly excited Na Rydberg atoms to vibrationally excited Na2 molecules

2001

Abstract We report the observation of the vibrational dependence of dissociative charge transfer (DCT), Na2(X1Σg+, v″) + Na∗∗(nl) → Na− + Na + Na+, in a single Na/Na2 supersonic beam at low intrabeam collision energies (1.6 meV) using the STIRAP technique for selective vibrational excitation of Na2 in the electronic ground state and time-of-flight mass analysis of the ions. The efficiency of this process increases by about an order of magnitude in the range 13 ≤ v″ ≤ 22. Some perspectives are discussed regarding the implementation of a field-free ion-imaging technique for the detection of ions that will allow the direct determination of the kinetic energy distributions of product negative i…

Light-Induced Protein-Matrix Uncoupling and Protein Relaxation in Dry Samples of Trehalose-Coated MbCO at Room Temperature

2005

In humid samples of trehalose-coated carboxy-myoglobin (MbCO), thermally driven conformational relaxation takes place after photodissociation of the carbon monoxide (CO) molecule at room temperature. In such samples, because of the extreme viscosity of the external matrix, photodissociated CO cannot diffuse out of the protein and explores the whole (proximal and distal side) heme pocket, experiencing averaged protein heme pocket structures, as a result of the presence of Brownian motions. At variance, in very dry samples, a lower portion of the photodissociated CO diffuses from the distal to the proximal heme pocket side probing in nonaveraged structures. We revisit here the flash photolysi…