Excimer lasers are currently being utilized as a means of photofragmentation and fragment excitation for chemical detection purposes. In the case of small hydrocarbons, this phenomenon is generally not well characterized and is poorly understood. Experiments aimed at a better understanding of the interaction of simple carbon-containing molecules with the ArF (193-nm) excimer laser and at exploring the potential analytical applications of this process are described. Specifically, carbon atoms were generated by multiphoton photolysis of CO, CH(4), C(2)H(2), C(3)H(8), CH(3)OH, and CH(3)COCH(3) using the ArF laser. Their presence was detected by two sensitive methods, laser-induced fluorescence (LIF) and resonance ionization emission spectroscopy (RIES), both of which take advantage of the coincident overlap between the ArF laser and the(1)D(2) ? (1)P(1)(0) transition at 193.1 nm with emission detection at 247.9 nm. The RIES method detects single photons resulting from the photolytically produced carbon ion recombination and relaxation processes. An enhancement in the RIES signal was observed when a second tunable laser pulse operating at 247.9 nm followed the ArF laser pulse. Both methods not only offer sensitive detection of the photolytic precursor molecules but also require only relatively simple experimental apparatus. Detection levels for the precursor molelcule considerably lower than 10(11)/cc for LIF and 10(12)/cc for RIES can be estimated based on the observed rates of signal production.
Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) 26-09-2005 REPORT TYPE Journal Article ABSTRACTThe efficient development of hypergolic fuels requires an interdisciplinary approach involving ab initio modeling, synthesis, and experimental physical chemistry. Candidate molecules must exhibit hypergolic ignition delay times that are fast enough to warrant further testing for safety and performance criteria. Hypergolic ignition delay apparatus has been mentioned in the open literature for six decades but accurate, detailed, modern ignition delay hardware that uses inexpensive laboratory building blocks and a minimum of custom circuitry is still needed. This paper details line-of-sight electro-optical circuitry with direct digital readout and additional oscilloscope recording that can be used to measure total ignition and chemical delay times for screening candidate fuels. We also illustrate the value of high speed video and quantum chemical calculations to supplement the ignition delay measurements for a comprehensive approach to hypergolic fuel research. The efficient development of hypergolic fuels requires an interdisciplinary approach involving ab initio modeling, synthesis, and experimental physical chemistry. Candidate molecules must exhibit hypergolic ignition delay times that are fast enough to warrant further testing for safety and performance criteria. Hypergolic ignition delay apparatus has been mentioned in the open literature for six decades, but accurate, detailed, modern ignition delay hardware that uses inexpensive laboratory building blocks and a minimum of custom circuitry is still needed. This article details line-of-sight electro-optical circuitry with direct digital readout and additional oscilloscope recording that can be used to measure total ignition and chemical delay times for screening candidate fuels. We also illustrate the value of high speed video and quantum chemical calculations to supplement the ignition delay measurements for a comprehensive approach to hypergolic fuel research.
A time-correlated single photon counting technique, coupled with a red sensitive photomultiplier tube, was used to determine the singlet-state lifetimes and energy transfer mechanisms of Chl a⋅H2O, (Chl a⋅H2O)2, and (Chl a⋅2H2O)n. The use of low concentrations and low incident light fluxes permitted measurements in a regime where nonlinear quenching effects are absent. The lifetimes exhibit a pronounced dependence on aggregate size. The results are examined in terms of exciton interactions in the excited singlet state of the Chl a aggregate. It is shown that in the absence of exciton annihilation effects, the rate of singlet-state decay via radiative coupling and intersystem crossing of a Chl a aggregate containing n equivalent monomeric units is equal to n times that of monomeric Chl a.
The long and interesting history of singlet delta ( 1 D g ) oxygen, including its discovery, study, understanding, and applications, has been described in several publications. [1±4] The singlet delta state is the lowest lying excited electronic state of oxygen and it differs from the triplet ground state, 3 AE g À ¹
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