摘要 :
A structural study based on EXAFS, FTIR, and optical absorption spectroscopies has been conducted on a photogenerated, metastable state of cyclopentadienylnickelnitrosyl (CpNiNO) produced by a reversible photochemical reaction. Th...
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A structural study based on EXAFS, FTIR, and optical absorption spectroscopies has been conducted on a photogenerated, metastable state of cyclopentadienylnickelnitrosyl (CpNiNO) produced by a reversible photochemical reaction. The photogenerated, metastable state with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was created by irradiating the sample with the 365 nm line of a mercury lamp at 20K . At the same temperature, the reverse reaction was induced by irradiation with the 313 nm line from the mercury lamp. Based on the analysis of the EXAFS data, the photogenerated, metastable state of CpNiNO has undergone considerable nuclear rearrangements compared to its ground state. The nuclear movement is characterized by a 0.12(angstrom) elongation of Ni-N bond and by a bending of Ni-N-O. A shift of the N-O stretching frequency from 1824 to 1387 cm(sup (minus)1) was observed in the photoinduced reaction with 365 nm light, implying that a NO(sup (minus)) like species results from intramolecular electron transfer from Ni to NO. The changes in the absorption spectra for the same reaction showed reduced absorption of the 385 nm band and a newly generated broad band near IR region. Temperature dependence of the Debye-Waller factor of CpNiNO was in good agreement with the diatomic harmonic oscillator for the Ni-N bond, but deviated for the Ni-O and the Ni-C bonds. Based on the structures obtained from EXAFS, ZINDO calculations for both the ground state and the photogenerated, metastable state of CpNiNO reproduced the general features of the observed absorption spectra and qualitatively explained the wavelength dependence of the reaction. The calculated partial charges on each atom in the ground state and the photogenerated, metastable state of CpNiNO are consistent with intramolecular electron transfer upon photoexcitation by 365 nm light.
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摘要 :
The structures of C(sub 5)H(sub 5)NiNO in a reversible photochemical reaction were studied via EXAFS, FTIR, and optical absorption spectroscopies. A photoexcited intermediate with distinctively different EXAFS, IR, and optical abs...
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The structures of C(sub 5)H(sub 5)NiNO in a reversible photochemical reaction were studied via EXAFS, FTIR, and optical absorption spectroscopies. A photoexcited intermediate with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was generated upon irradiation using 365 mn light at 20K in a 3-methylpentane solution. The reverse reaction was induced by irradiation with 310 mn light. The EXAFS data analysis has shown a 0.12 (Angstrom) elongation of the Ni-N bond and the bending, of Ni-N-0 in the photoexcited intermediate. Several ZINDO calculations were conducted based on the structures obtained from the EXAFS spectroscopy. These calculations reproduced the changes in the optical spectra and the intramolecular electron transfer in C(sub 5)H(sub 5)NiNO.
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摘要 :
The structures of C(sub 5)H(sub 5)NiNO in a reversible photochemical reaction were studied via EXAFS, FTIR, and optical absorption spectroscopies. A photoexcited intermediate with distinctively different EXAFS, IR, and optical abs...
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The structures of C(sub 5)H(sub 5)NiNO in a reversible photochemical reaction were studied via EXAFS, FTIR, and optical absorption spectroscopies. A photoexcited intermediate with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was generated upon irradiation using 365 mn light at 20K in a 3-methylpentane solution. The reverse reaction was induced by irradiation with 310 mn light. The EXAFS data analysis has shown a 0.12 (Angstrom) elongation of the Ni-N bond and the bending, of Ni-N-0 in the photoexcited intermediate. Several ZINDO calculations were conducted based on the structures obtained from the EXAFS spectroscopy. These calculations reproduced the changes in the optical spectra and the intramolecular electron transfer in C(sub 5)H(sub 5)NiNO.
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摘要 :
In general a variable repetition rate of the x-ray bunches is needed to explore time domain problems using x-ray radiation. In some instances the results of several hundreds or thousands of x-ray pulses must be averaged requiring ...
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In general a variable repetition rate of the x-ray bunches is needed to explore time domain problems using x-ray radiation. In some instances the results of several hundreds or thousands of x-ray pulses must be averaged requiring the sample to be in the same time dependent state each time the monitoring pulse strikes. In the most advanced and most detailed version of this type experiment an intense laser pulse would be used to create an excited state from a relaxed ground state. An additional ''probe-pulse'' that follows the laser ''pump-pulse'' would examine the sample. The important point is that before a second x-ray pulse hits the sample, the system must return to its initial relaxed ground state prior to another laser pulse in order to prepare the same excited state again. Otherwise the second x-ray probes a different condition of the system than the previous x-ray bunch such that any data averaging scheme would be invalid. Our system is primarily designed for the Advanced Photon source (APS) at Argonne National Laboratory. In the 20-bunch mode of APS an x-ray pulse will occur every 177 nanoseconds, requiring each edge of a conventional two-blade ''shutter'' to travel at least 0.25 mm in (approximately)177 nanoseconds. Our key design principle employs a subsonic, rotating mirror whose period is slaved to the synchrotron intra-pulse period. The synchrotron x-ray bunches will be reflected a distance of about two meters to a narrow 0.5 mm slit just in front of the sample. The time that the reflected synchrotron spends striking the slit is given by 1/(4(pi)rf) where r is the radius from the center of the spindle to the slit, and f is the frequency of rotation of the spindle. A mirror rotating at a low 7,500 rpm (125 Hz) is sufficient to select a single synchrotron pulse. The very precise phase stability required by this method is currently available in rotating mirror devices for laser scanning. 11 refs., 2 figs.
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摘要 :
The authors have applied the high-power ESE technique to primary photosynthesis observing stationary state signals arising from the primary donor, the primary acceptors, and the triplet state observed in R. rubrum. In addition, th...
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The authors have applied the high-power ESE technique to primary photosynthesis observing stationary state signals arising from the primary donor, the primary acceptors, and the triplet state observed in R. rubrum. In addition, the authors have performed nanosecond time-resolved ESE-EPR studies of green plant photosynthesis. ESE is a form of pulsed high-power EPR. Thus, systems studied by EPR are usually suitable for study by ESE. The ESE method employs repetitive trains of two or three intense microwave pulses to induce signals in paramagnetic samples known as echoes. The authors ESE spectrometer utilizes ten-watt microwave pulses, 20 to 60 nsec wide. The most common pulse sequence is the 90 exp 0 , T, 180 exp 0 two-pulse sequence where T is the time between the two pulses. In the authors spectrometer the 90 exp 0 pulse (P sub 90 ) is approximately 30 nsec wide. Before P sub 90 the net magnetization M/sub z/ is aligned only along the external magnetic field direction z. P sub 90 , as its name implies, rotates the resonant electron spins of M/sub z/ 90 exp 0 such that immediately after the pulse these spins are in the x,y plane normal to the magnetic field. (ERA citation 04:008888)
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