Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our pre...Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our previous work [Acta Phys. Sin. 61 174301 （2012）], an analytical model to predict the sound absorption from vibrational relaxation in a gas medium is proposed. In this paper, we develop the model to decouple the V-V coupled energy to each vibrationaltranslational deexcitation path, and analyze how the multimode relaxations form the peaks of sound absorption spectra in gas mixtures. We prove that a multimode relaxation is the sum of its decoupled single-relaxation processes, and only the decoupled process with a significant isochoric-molar-heat can be observed as an absorption peak. The decoupling model clarifies the essential processes behind the peaks in spectra arising from the multimode relaxations in multi-component gas mixtures. The simulation validates the proposed decoupling model.展开更多
Results from simulations of plasma and neutrals under conditions predictively characterizing the detached plasma regime in the linear machine MAGNUM-PSI are presented. The relaxation of the vibrationally excited hydro...Results from simulations of plasma and neutrals under conditions predictively characterizing the detached plasma regime in the linear machine MAGNUM-PSI are presented. The relaxation of the vibrationally excited hydrogen molecules is investigated in order to establish a relation between their relaxation and dwell times, and the role of the varions mechanisms of the molecular vibrational kinetics. Tile results obtained show that the individual vibrational states have to be inclllded in the transport code for neutrals as distinct species, since the relaxation time of tile vibrational states is sufficiently longer than the typical dwell time of hydrogen molecules in the detached plasma region. The parameters of plasma and neutrals are affected by the transport of the vibrationally excited hydrogen lnolecnles. Furthermore. the rate of molecular reconlbination is overestimated by a factor of - 5 provided that the transport of ilydrogen molecules only in their ground vibrational state is considered. The role of the various processes of vibrational kinetics is studied. The vibrational excitation through singlet electronic states ires a strong influence on the molecular densities for levels with vibrational quantum numbers v≥ 5. Vibration-vibration （V-V） collisions between vibrationally excited hydrogen molecules and vibration-translation （V-T） collisions between vibrationally excited hydrogen molecules and ground state molecules and atoms are of nlinor importance in MAGNUM-PSI.展开更多
A theoretical model of chemical and vibrational kinetics of hydrogen oxidation is suggested based on the consistent account for the vibrational nonequilibrium of HO2 radical which forms in result of bimolecular recomb...A theoretical model of chemical and vibrational kinetics of hydrogen oxidation is suggested based on the consistent account for the vibrational nonequilibrium of HO2 radical which forms in result of bimolecular recombination H + O2 = HO2 in the vibrationally excited state. The chain branching H + O2 = O + OH and inhibiting H + O2 + M = HO2 + M formal reactions are considered (in the terms of elementary processes) as a general multi-channel process of forming, intramolecular energy redistribution between modes, relaxation, and monomolecular decay of the comparatively long-lived vibrationally excited HO2 radical which is capable to react and exchange of energy with another components of the mixture. The model takes into account the vibrational nonequilibrium for the starting (primary) H2 and O2 molecules, as well as the most important molecular intermediates HO2, OH, O2(1D), and the main reaction product H2O. The calculated results are compared with the shock tube experimental data for strongly diluted H2-O2 mixtures at 1000 T p < 4 atm. It is demonstrated that this approach is promising from the standpoint of reconciling the predictions of the theoretical model with experimental data obtained by different authors for various compositions and conditions using different methods. It is shown that the hydrogen-oxygen reaction proceeds in absence of vibrational equilibrium, and the vibrationally excited HO2 radical acts as a key intermediate in the principally important chain branching process. For T < 1500 K, the nature of hydrogen-oxygen reaction is especially nonequilibrium, and the vibrational nonequilibrium of HO2 radical is the essence of this process.展开更多
Operation of a laser-driven nano-motor inevitably generates a non-trivial amount of heat, which can possibly lead to instability or even hinder the motor＇s continual running. This work quantitatively examines the ove...Operation of a laser-driven nano-motor inevitably generates a non-trivial amount of heat, which can possibly lead to instability or even hinder the motor＇s continual running. This work quantitatively examines the overheating problem for a recently proposed laser-operated molecular locomotive. We present a single-molecule cooling theory, in which molecular details of the locomotive system are explicitly treated. This theory is able to quantitatively predict cooling efficiency for various candidates of molecular systems for the locomotive, and also suggests concrete strategies for improving the locomotive＇s cooling. It is found that water environment is able to cool the hot locomotive down to room temperature within 100 picoseconds after photon absorption. This cooling time is a few orders of magnitude shorter than the typical time for laser operation, effectively preventing any overheating for the nano-locomotive. However, when the cooling is less effective in non-aqueous environment, residual heat may build up. A continuous running of the motor will then lead to a periodic thermodynamics, which is a common character of many laser-operated nano-devices.展开更多
The excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical...The excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical calculations.Conformational conversion from the syn-enol configuration to the keto configuration is proposed as the mechanism of excited-state intramolecular proton transfer.The duration of excited-state intramolecular proton transfer is measured to range from 50 fs to 200 fs in different solvents.This time is strongly dependent on the calculated energy gap between the N-S;and T-S;structures in the S;state.Along the proton transfer reaction coordinate,the vibrational relaxation process on the S;state potential surface is observed.The duration of the vibrational relaxation process is determined to be from8.7 ps to 35 ps dependent on the excess vibrational energy.展开更多
The vibration- translational relaxation ime of ozone (001) was measured from phase delay of the photoacoustic detected signal with respect to signal of CO2-laser radiation in the binary mixtures of O3 with N2, O2, an...The vibration- translational relaxation ime of ozone (001) was measured from phase delay of the photoacoustic detected signal with respect to signal of CO2-laser radiation in the binary mixtures of O3 with N2, O2, and Ar at the temperature 300°K. To eliminate the phase delay of the detected signal caused by inertia of the microphone membrane the technique of electrical activation was used.展开更多
The integral cross sections and rate constants of pure rotational and ro-vibrational energy transfer processes for the Ar-HF system are thoroughly studied by using the timeindependent close coupling method based on ou...The integral cross sections and rate constants of pure rotational and ro-vibrational energy transfer processes for the Ar-HF system are thoroughly studied by using the timeindependent close coupling method based on our newly constructed potential energy surface. Compared to previous theoretical results, pure rotational transitions in this work achieve better agreement with the experimental data. For ro-vibrational energy transfer, it is found that quasi-resonant transitions dominate the cross sections in all cases. Furthermore, the vibrational-resolved rate constant of transition v=1→v=0 increases very quickly with the temperature from 100K to 1500K and is also in good agreement with the available experimental results.展开更多
When femtosecond （fs） timeresolved experiments are used to study ultrafast processes, quantum beat phenomena are often observed. In this paper, to analyze the fs timeresolved spectra, we will present the density mat...When femtosecond （fs） timeresolved experiments are used to study ultrafast processes, quantum beat phenomena are often observed. In this paper, to analyze the fs timeresolved spectra, we will present the density matrix method, a powerful theoretical technique, which describes the dynamics of population and coherence of the system. How to employ it to study the pumpprobe experiments and fs ultrafast processes is described. The transition of pyrazine is used as an example to demonstrate the application of the density matrix method. Recently, Suzuki＇s group have employed the 22 fs time resolution laser to study the dynamics of the state of pyrazine. In this case, conical intersection is commonly believed to play an important role in this nonadiabatic process. How to treat the effect of conical intersection on nonadiabatic processes and fs timeresolved spectra is presented. Another important ultrafast process, vibrational relaxation, which takes place in subps and ps range and has never been carefully studied, is treated in this paper. The vibrational relaxation in water dimer is chosen to demonstrate the calculation. It should be noted that the vibrational relaxation of （H20）2 has not been experimentally studied but it can be accomplished by the pump-probe experiments.展开更多
To research the correlation between vibrational energy transition rates and acoustic relaxation processes in excitable gases, the vibrational relaxation theory provided by Tanczos [J. Chem. Phy3. 25, 439 （1956）] is ...To research the correlation between vibrational energy transition rates and acoustic relaxation processes in excitable gases, the vibrational relaxation theory provided by Tanczos [J. Chem. Phy3. 25, 439 （1956）] is applied to calculate the energy transition rates of Vibrational- Vibrational （V-V） and Vibrational-Translational （V-T） energy transfer in gas mixtures. The results of calculation for the multi-relaxation processes in various gas mixtures, consisting of carbon dioxide, methane, chlorine, nitrogen, and oxygen at room temperature, demonstrate that the acoustic energy stagnated in every vibrational mode is coupled with each other through V-V energy exchanges. The vibrational excitation energy will relax through the V-T de-excitation path of the lowest mode because of its fastest V-T transition rate, resulting in that only one absorption peak can be measured for most of excitable gas mixtures. Thus, an effective model is provided to analyze how the vibrational energy transition rates affect the characteristics of acoustic relaxation processes and acoustic propagation in excitable gas mixtures.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60971009 and 61001011)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090142110019)+1 种基金the Natural Science Foundation of Hubei Province, China (Grant No. 2010CDB02701)the Fundamental Research Funds for the Central Universities, China (Grant No. 2012QN083)
文摘Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our previous work [Acta Phys. Sin. 61 174301 （2012）], an analytical model to predict the sound absorption from vibrational relaxation in a gas medium is proposed. In this paper, we develop the model to decouple the V-V coupled energy to each vibrationaltranslational deexcitation path, and analyze how the multimode relaxations form the peaks of sound absorption spectra in gas mixtures. We prove that a multimode relaxation is the sum of its decoupled single-relaxation processes, and only the decoupled process with a significant isochoric-molar-heat can be observed as an absorption peak. The decoupling model clarifies the essential processes behind the peaks in spectra arising from the multimode relaxations in multi-component gas mixtures. The simulation validates the proposed decoupling model.
基金the European Communities under the contract of Association between EURATOM/FOM
文摘Results from simulations of plasma and neutrals under conditions predictively characterizing the detached plasma regime in the linear machine MAGNUM-PSI are presented. The relaxation of the vibrationally excited hydrogen molecules is investigated in order to establish a relation between their relaxation and dwell times, and the role of the varions mechanisms of the molecular vibrational kinetics. Tile results obtained show that the individual vibrational states have to be inclllded in the transport code for neutrals as distinct species, since the relaxation time of tile vibrational states is sufficiently longer than the typical dwell time of hydrogen molecules in the detached plasma region. The parameters of plasma and neutrals are affected by the transport of the vibrationally excited hydrogen lnolecnles. Furthermore. the rate of molecular reconlbination is overestimated by a factor of - 5 provided that the transport of ilydrogen molecules only in their ground vibrational state is considered. The role of the various processes of vibrational kinetics is studied. The vibrational excitation through singlet electronic states ires a strong influence on the molecular densities for levels with vibrational quantum numbers v≥ 5. Vibration-vibration （V-V） collisions between vibrationally excited hydrogen molecules and vibration-translation （V-T） collisions between vibrationally excited hydrogen molecules and ground state molecules and atoms are of nlinor importance in MAGNUM-PSI.
文摘A theoretical model of chemical and vibrational kinetics of hydrogen oxidation is suggested based on the consistent account for the vibrational nonequilibrium of HO2 radical which forms in result of bimolecular recombination H + O2 = HO2 in the vibrationally excited state. The chain branching H + O2 = O + OH and inhibiting H + O2 + M = HO2 + M formal reactions are considered (in the terms of elementary processes) as a general multi-channel process of forming, intramolecular energy redistribution between modes, relaxation, and monomolecular decay of the comparatively long-lived vibrationally excited HO2 radical which is capable to react and exchange of energy with another components of the mixture. The model takes into account the vibrational nonequilibrium for the starting (primary) H2 and O2 molecules, as well as the most important molecular intermediates HO2, OH, O2(1D), and the main reaction product H2O. The calculated results are compared with the shock tube experimental data for strongly diluted H2-O2 mixtures at 1000 T p < 4 atm. It is demonstrated that this approach is promising from the standpoint of reconciling the predictions of the theoretical model with experimental data obtained by different authors for various compositions and conditions using different methods. It is shown that the hydrogen-oxygen reaction proceeds in absence of vibrational equilibrium, and the vibrationally excited HO2 radical acts as a key intermediate in the principally important chain branching process. For T < 1500 K, the nature of hydrogen-oxygen reaction is especially nonequilibrium, and the vibrational nonequilibrium of HO2 radical is the essence of this process.
基金supported by the National Natural Science Foundation of China (Grant No 90403006)Chinese Ministry of Education (the Programme for New Century Excellent Talents in University)+1 种基金Shanghai Education Development Foundation of China (the Shuguang Programme)Shanghai Pujiang Programme of China (Grant No 05PJ14019)
文摘Operation of a laser-driven nano-motor inevitably generates a non-trivial amount of heat, which can possibly lead to instability or even hinder the motor＇s continual running. This work quantitatively examines the overheating problem for a recently proposed laser-operated molecular locomotive. We present a single-molecule cooling theory, in which molecular details of the locomotive system are explicitly treated. This theory is able to quantitatively predict cooling efficiency for various candidates of molecular systems for the locomotive, and also suggests concrete strategies for improving the locomotive＇s cooling. It is found that water environment is able to cool the hot locomotive down to room temperature within 100 picoseconds after photon absorption. This cooling time is a few orders of magnitude shorter than the typical time for laser operation, effectively preventing any overheating for the nano-locomotive. However, when the cooling is less effective in non-aqueous environment, residual heat may build up. A continuous running of the motor will then lead to a periodic thermodynamics, which is a common character of many laser-operated nano-devices.
基金supported by the Natural Science Foundation of Hubei Province,China(Grant No.2020CFB468)the Guiding Project of Scientific Research Plan of Department of Education of Hubei Province,China(Grant No.B2020136)+1 种基金the National Key Research and Development Program of China(Grant No.2019YFA0307700)the National Natural Science Foundation of China(Grant Nos.11974381,11674355,and 21507027)。
文摘The excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical calculations.Conformational conversion from the syn-enol configuration to the keto configuration is proposed as the mechanism of excited-state intramolecular proton transfer.The duration of excited-state intramolecular proton transfer is measured to range from 50 fs to 200 fs in different solvents.This time is strongly dependent on the calculated energy gap between the N-S;and T-S;structures in the S;state.Along the proton transfer reaction coordinate,the vibrational relaxation process on the S;state potential surface is observed.The duration of the vibrational relaxation process is determined to be from8.7 ps to 35 ps dependent on the excess vibrational energy.
文摘The vibration- translational relaxation ime of ozone (001) was measured from phase delay of the photoacoustic detected signal with respect to signal of CO2-laser radiation in the binary mixtures of O3 with N2, O2, and Ar at the temperature 300°K. To eliminate the phase delay of the detected signal caused by inertia of the microphone membrane the technique of electrical activation was used.
基金supported by the National Natural Science Foundation of China (No.21590802 and No.21733006)
文摘The integral cross sections and rate constants of pure rotational and ro-vibrational energy transfer processes for the Ar-HF system are thoroughly studied by using the timeindependent close coupling method based on our newly constructed potential energy surface. Compared to previous theoretical results, pure rotational transitions in this work achieve better agreement with the experimental data. For ro-vibrational energy transfer, it is found that quasi-resonant transitions dominate the cross sections in all cases. Furthermore, the vibrational-resolved rate constant of transition v=1→v=0 increases very quickly with the temperature from 100K to 1500K and is also in good agreement with the available experimental results.
文摘When femtosecond （fs） timeresolved experiments are used to study ultrafast processes, quantum beat phenomena are often observed. In this paper, to analyze the fs timeresolved spectra, we will present the density matrix method, a powerful theoretical technique, which describes the dynamics of population and coherence of the system. How to employ it to study the pumpprobe experiments and fs ultrafast processes is described. The transition of pyrazine is used as an example to demonstrate the application of the density matrix method. Recently, Suzuki＇s group have employed the 22 fs time resolution laser to study the dynamics of the state of pyrazine. In this case, conical intersection is commonly believed to play an important role in this nonadiabatic process. How to treat the effect of conical intersection on nonadiabatic processes and fs timeresolved spectra is presented. Another important ultrafast process, vibrational relaxation, which takes place in subps and ps range and has never been carefully studied, is treated in this paper. The vibrational relaxation in water dimer is chosen to demonstrate the calculation. It should be noted that the vibrational relaxation of （H20）2 has not been experimentally studied but it can be accomplished by the pump-probe experiments.
基金supported by the National Natural Science Foundation of China(61461008,61371139,61571201,61540051)the China Scholarship Council Project(201708525058)+1 种基金the National Science Foundation of Guizhou Province,China(Qian Ke He J Zi[2015]2065),Qian Ke He LH Zi[2014]7361)the Recruitment Program of Guizhou Institute of Technology(XJGC20140601,XJGC20150107)
文摘To research the correlation between vibrational energy transition rates and acoustic relaxation processes in excitable gases, the vibrational relaxation theory provided by Tanczos [J. Chem. Phy3. 25, 439 （1956）] is applied to calculate the energy transition rates of Vibrational- Vibrational （V-V） and Vibrational-Translational （V-T） energy transfer in gas mixtures. The results of calculation for the multi-relaxation processes in various gas mixtures, consisting of carbon dioxide, methane, chlorine, nitrogen, and oxygen at room temperature, demonstrate that the acoustic energy stagnated in every vibrational mode is coupled with each other through V-V energy exchanges. The vibrational excitation energy will relax through the V-T de-excitation path of the lowest mode because of its fastest V-T transition rate, resulting in that only one absorption peak can be measured for most of excitable gas mixtures. Thus, an effective model is provided to analyze how the vibrational energy transition rates affect the characteristics of acoustic relaxation processes and acoustic propagation in excitable gas mixtures.
