@phdthesis{oai:nagoya.repo.nii.ac.jp:00009424,
 author = {中山, 智喜 and Nakayama, Tomoki},
 month = {Mar},
 note = {Photochemical reactions of free radical play a crucial role in determinlng chemical composition of the atmosphere. Odd nitrogen radicals (NOx = N + NO + NO_2)and odd hydrogen radicals (HOx = H + OH + HO_2) are important in the middle and upper atmosphere. For example, the catalytic cycle including NOx is a major removal process of ozone in the lower and middle stratosphere, and the catalytic cycle including HOx becomes dominant O_3 sink in the upper stratosphere and mesosphere. Therefore, it is important for a reliable assessment of the ozone trend to understand the photochemical processes of NOx and HOx.  In this study, the laboratory studies on several new important processes of NOx and HOx in the middle and upper atmosphere have been performed using laser spectroscopic techniques. A new technique for high-sensitive detection of the electronic ground state nitrogen atom, N(4S), and the electronica11y excited oxygen atom, 0(1S), has been developed in this study. The N(4S) atoms were detected by vacuum ultraviolet laser-induced fluorescence (VUV-LIF) techinique at 120.07nm which is resonant with the electronic transition N3s4Pl/2←2p4S3/2. The subsequent  fluorescence  from the excited state is directly observed by a solar-blind photomultiplier.  Tunable VUV radiation around 120.07nm was generated by two-photon resonance four-wave sum frequency mixing in Hg vapor. The O(1S) atoms were detected by VUV-LIF technique at 121.76nm which is resonant with the electronic transition O(3S1pP_1← 2p1S_o). Tunable VUV radiation around 121.76nm was generated by two-Photon resonance four-wave difference frequency mixing in a gas mixture of Kr/Ar.  The VUV-LIF technique utilized in this study has a minimum sensitivity of 2×10^9 and 3× 10^8 atoms cm^{-3} for detections of N(4S) and O(1S), respectively.In Chapter3, the formation of N(4S) from the UV photolysis of Nitrous oxide N_20)and impact on NOx formation in the stratosphere has been described.  N_20 is known to be a precursor of NOx in the stratosphere. Most of stratospheric removal of N_20 transported through planetary boundary layer and the free troposphere to the stratosphere is photolysis by the solar UV radiation around 200nm, while a small fraction of N_20 reacts with O(1D)atoms. Stratospheric NOx production is thought to be due to the reaction of N_20 with O(1D). If the photodissociation channel of N_20 to produce N(4S) + NO exist with a significant yield, it could be a new source of NOx in the stratosphere. In the present study, the quantum yield for N(4S) formation from N_20 photolysis has been determined to be(2･1±0.9)×10^{-3} at 193nm.  A sensitivity analysis to assess the impact of the N(4S) and NO formation from N_20 photolysis on stratospheric chemistry has been performed using a one-dimensional photochemical model. When considering the N(4S) + NO channel as an additional photolytic sink of N_20, the steady state NOx concentration increases up to～3% around 25 km in comparison with that ignoring the N(4S) + NO channel. In Chapter 4, the reaction kinetics of N(4S)atoms with NOx have been described. The reaction of N(4S) with NO is though to act as a sink of NOx in the upper stratosphere, mesosphere and thermosphere.  The experimental technique of  laser flush photolysis and the VUV-LIF detection was applied for the first time to the kinetic studies of the reactions involving N(4S). The N(4S) atoms were produced following 193nm ArF laser irradiation of NO and NO_2. The photoexcitation processes of NO  and NO_2 giving rise to the N(4S)formation have been discussed in detail.Based on the measurements of Doppler profiles of N(4S)atoms and photolysis laser power dependence of the N(4S)LIF intensity, the N(4S)formation from NO occurs predissociatively following one-photon absorption, while that from NO_2 includes two-Photon processes. The rate constants for the reactions of N(4S)with NO and NO_2 at 295 ± 2K have been determined to be (3.8±0.2)×10^{-11}and(7･3±0･9)×10^{-12} cm^3 molecules^{-1}s^{-1}, respectively. Those results are compared with the literature data.In Chapter 5, the collisional relaxation processes of suprathermal N(4S)atoms, which are relevant to NO formation in the thermosphere, have been described. Although it had been proposed that a significant amount of lower-thermospheric NO molecules came from the reaction of suprathermal N(4S)atoms with O_2, no experimental evidence of the reaction was available. The reaction barrier of the N(4S) reaction with O_2 was reported to be ～0･24eV.  In this study, the competitive processes of the inelastic collisions to produce NO and the elastic collisions to thermalize the translational energy of N(4S)have been investigated for the reaction of suprathermal N(4S)reaction with O_2 at initial center-of-mass collision energy of about 0.24-0.6eV.  The suprathermal N(4S) atoms which have an average translational energy of  0.92 ± 0.095 eV in the laboratory flame were produced by 193 nm photolysis of NO_2 in bath gas of O_2. Doppler profiles of the N(4S)atoms were recorded by VUV-LIF detection of N(4S), from which the average kinetic energy of the N(4S) atoms were obtained as a function of thermalization time. No clear evidence of the NO production has been observed, which will be explained by a relatively large value of the thermalization cross section compared with the inelastic collision cross section.Monte-Carlo calculations employing an elastic hard-sphere collision model have been performed to estimate the hard-sphere collision radii and thermalization cross section. The themalization cross section, which reproduced the experimental results, were (3.8±0.4),(2.8±0.4),(1.8±0.2), and (2.3±0.2) in units of 10^15cm^2 for N(4S)+ N_2, 0_2, He and Ar, respectively.  The thermalization cross sections will make it possible to perform more precise model calculations for NO formation processes in the thermosphere.In Chapter 6, the photolytic formation of O(1S) from the UV photolysis of O_3 around 200 nm and its subsequent reactions with small molecules relevant to middle and upper atmospheric chemistry have been studies, and impact on HOx formation in the stratosphere and mesosphere through O(1S) + H_2O reaction has been described.  The quantum yield for O(1S) formation from O_3 photolysis at 295 K has been determined to be (2.5 ± 1.1)×10^-3, (1.4±0.4)×10^{-4} and (5±3)×10^{-5}, at 193,215 and 220nm, respectively.  The rate constants for the reactions of O(1S) with O_2, CO_2, H_2O, O_3 and HC1 at 295 ± 2K have been determined to be (2.85±0.31)×10^{-13}, (3.09±0.29) ×10^{-13},　(6.38±0.38)×10^{-10}, (4.63±0.45)×10^{-10} and (5.47±0.27)×10^{-10}　cm^3 molecules^{-1}s^{-1}, respectively. Based on the present laboratory data we obtained, impact of the O(1S) formation from O_3 photolysis on the OH radial formation in the stratosphere and mesosphere has been investigated. It has been concluded that, the reaction of H_2O with O(1S) produced from O_3 photolysis around 200 nm provides a new source of OH in the stratosphere and mesosphere, which is up to ～2･5% of the conventional OH production by O(1D) + H_2O reaction at 30 Km altitude in mid-latitude.  Implications of the present results for the terrestrial airglow of O(1S) at 557.7nm have also been discussed.  It has been suggested that the impact of the direct formation of O(1S) from O_3 photolysis on the volume emission rate is less significant than the formation through the previously proposed Barth mechanism.The results in this thesis show that the photolytic formation of N(4S) and NO from N_2O can act as a new source of stratospheric NOx, and that the reaction of H_2O with O(1S) which is formed from O_3 photolysis can act as a new source of stratospheric and mesospheric HOx. These new NOx and HOx sources should be taken into account for detail understanding of the chemical processes in the middle and upper atmosphere.  The results also demonstrate that the VUV-LIF technique which developed in the present study is a powerful tool to investigate both the photodissociation of small molecules and the kinetics involving N(4S) and O(1S) atoms., 名古屋大学博士学位論文 学位の種類:博士(理学) (課程) 学位授与年月日:平成18年3月27日},
 school = {名古屋大学, Nagoya University},
 title = {Laboratory studies of new photochemical processes of NOx and HOx in the middle and upper atmosphere},
 year = {2006}
}