Competition between HF And HCl molecular elimination in IRMPD of 1,2-dichloro-1,2-difluoroethane

The infrared multiple-photon decomposition of 1,2-dichloro-1,2-difluoroethane has been studied using time-resolved infrared emission. Vibrationally excited parent molecules dissociate competitively via two channels to form vibrationally excited HCl and HF, depending strongly on CO₂ laser fluence. The yield of HF elimination increases with fluence, while that of HCl elimination reaches a plateau and then decreases.     

2P12 excited iodine formation in the F + HI reaction

Fluorine atoms produced in a microwave discharge of SF₆ were mixed with HI molecules in a flow system. Groundstate and excited iodine atoms were monitored by measuring the absorption of atomic emission lines from an iodine resonance lamp. A model taking into account the formation of excited iodine atoms through the reactive channel as well as the VE energy transfer process from vibrationally excited HF molecules is discussed. The fraction of excited iodine atoms formed in the reaction is shown to be 0.5.     

Dependence of the Interaction Potentials of Ar-HF and N2-HF on HF Bond Length

We explore in detail the nature of the intermolecular interactions in two HF containing complexes, ArHF and N₂ HF, at vibrationally excited HF stretching states using both high overtone spectroscopic and ab initio computational methods. By using an infrared intracavity laser-induced fluorescence technique, second overtone spectra of the two HF complexes have been obtained for the HF stretches and their combination modes with low-frequency van der Waals vibrations. The two complexes show the same trend that both van der Waals bond strength and rotational constant increase smoothly with v of the HF stretch. The investigation of the intermolecular potential above minimum provides a rigorous test of ab initio calculations. In particular for the ab initio calculations using an efficient basis set incorporating bond functions, the technique reproduces reasonably well the anisotropy of the interaction potential of Ar and HF. It is found that the intermolecular potential depends strongly upon the HF bond length only at the linear Ar-H-F geometry.     

Experimental Study of C2Cl3+NO2 Reaction

The free radical reaction of C2Cl3 with NO2 was investigated by step-scan time-resolved FTIR (TR-FTIR) emission spectroscopy. Due to the vibrationally excited products of Cl2CO, NO, and CO, strong IR emission bands were observed with high resolution TR-FTIR spectra. Four reaction channels forming C2Cl3O+NO, CCl3CO+NO, CO+NO+CCl3, and ClCNO+Cl2CO were elucidated, respectively. Spectralˉtting showed that the product CO was highly vibrationally excited with the nascent average vibrational energy of 60.2 kJ/mol. Possible reaction mechanism via intermediates C2Cl3NO2 and C2Cl3ONO was proposed.     

Time‐Resolved FTIR Emission Spectroscopy of Transient Radicals

Fourier Transform spectroscopy with 10^?8 second time resolution for recording IR emission spectra has been developed as an efficient means for detecting previously unknown vibrational modes of transient radicals. 193 nm photodissociation of a precursor molecule is used to generate vibrationally excited radicals, from which IR emission is recorded with time and spectral resolution. Assignment of the spectra is performed using information obtained through multiple precursors, isotopic substitution, time dependence of emission intensity, theoretical calculations, and 2‐dimensional cross‐spectra correlation analysis. The radicals vinyl, cyanovinyl, and OCCN have been studied with many vibrational modes identified.     

IR and visible luminescence studies in the infrared multiphoton dissociation of 1,2-dibromo-1,1-difluoroethane

The infrared multiphoton dissociation of 1,2-dibromo-1,1-difluoroethane gives rise to IR and visible luminescence. Vibrationally excited parent molecules dissociate via two primary channels yielding bromine and vibrationally excited HBr. The strong visible emission observed between 350 to 750 nm has been assigned to electronically excited carbene CF₂Br H.     

Vibrationally promoted electron emission from low work-function metal surfaces

We observe electron emission when vibrationally excited NO molecules with vibrational state v, in the range of 9 < or = v < or =18, are scattered from a Cs-dosed Au surface. The quantum efficiency increases strongly with v, increasing up to 10(-2) electrons per NO (v) collision, a value several orders of magnitude larger than that observed in experiments with similar molecules in the ground vibrational state. The electron emission signal, as a function of v, has a threshold where the vibrational excitation energy slightly exceeds the surface work function. This threshold behavior strongly suggests that we are observing the direct conversion of NO vibrational energy into electron kinetic energy. Several potential mechanisms for the observed electron emission are explored, including (1) vibrational autodetachment, (2) an Auger-type two-electron process, and (3) vibrationally promoted dissociation. The results of this work provide direct evidence for nonadiabatic energy-transfer events associated with large amplitude vibrational motion at metal surfaces.     

Optical analysis of the light emission from porous silicon: a hybrid polyatom surface-coupled fluorophor

The most extensive data set yet generated correlating photoluminescence excitation (PLE) and photoluminescence (PL) spectra is presented for aged (equilibrated) porous silicon (PS) samples. The observed features, which are temperature independent over the range 10-300 K, show a detailed correlation with the results of photoacoustic spectroscopy (PAS) and with molecular electronic structure calculations. The observed energy level patterns are reproduced in the photoabsorption (PA) of PS films released after the etching of a silicon wafer. It is concluded that the energy level pattern found for the photoluminescing surface of PS results from a structure which is neither uniquely molecule- or bulk-like but represents a hybrid form for which the density of states associated with a polyatomic vibrationally excited surface-bound fluorophor dominates the nature of the observed features which are not those of a semiconductor. These fluorophor features are broadened and shifted to lower excitation energy as a result of the intimate presence of the silicon surface to which the fluorophor is bound. The dominance of the surface-bound fluorophor accounts for the temperature-independent PLE and PL features. The observed spectral features are thus suggested to be the result of a strong synergistic interaction in which the silicon surface influences the location of surface-bound fluorophor excited states whereas the nature of the vibrationally excited surface-bound fluorophor coupling to the silicon surface provides the mechanism for an enhanced vibronic structure dominated interaction and energy transfer. The observed PLE, PL, PAS, and PA measurements are found to be consistent with previous photovoltaic and photoconductivity measurements, correlating well with a surface-bound oxyhydride-like emitter. This study suggests the important role that the overtone structure of a molecule bound to a surface can play as one forms a hybrid system.     

Photolysis (193 nm) of SO2: nascent product energy distribution examined through IR emission

Infrared emission following the photolysis of SO(2) by a 193 nm laser pulse (20 ns duration) was recorded with 500 ns time and 10 cm(-1) spectral resolution. Spectral analyses of the time-resolved spectra revealed the vibrationally excited nascent SO population distribution as (v = 1)/(v = 2)/(v = 3)/(v = 4)/(v = 5) = 0.54 ± 0.04, 1.00 ± 0.03, 0.00 ± 0.03, 0.01 ± 0.03, and 0.10 ± 0.03. The nascent SO was found to be rotationally excited with an average rotational temperature around 1000 K for v = 1 and v = 2 levels and 300 K for the v = 5 level. The vibrationally excited SO likely originates from two distinct dissociation mechanisms; the v = 1 and 2 populations are generated through intersystem crossing between the C state and a repulsive state (2(3)A'), and the v = 5 population is generated through internal conversion from the C to the X state. Efficient V-V energy transfer from nascent vibrationally excited SO to SO(2)(ν(1)) is also observed. The appearance of the SO(2)(ν(1)) ν(1) = 2 emission, before that from the ν(1) = 1 population is consistent with the previous report that the Δν = -2 channel is more efficient than the Δν = -1 channel.     

A dispersed fluorescence and ab initio investigation of the X2B1 and A2A1 electronic states of the PH2 molecule

In this work, the X2B1 and A2A1 electronic states of the phosphino (PH2) free radical have been studied by dispersed fluorescence and ab initio methods. PH2 molecules were produced in a molecular free-jet apparatus by laser vaporizing a silicon rod in the presence of phosphine (PH3) gas diluted in helium. The laser-induced fluorescence, from the excited A2A1 electronic state down to the ground electronic state, was dispersed and analyzed. Ten (upsilon1upsilon2upsilon3) vibrationally excited levels of the ground electronic state, with upsilon1 < or = 2, upsilon2 < or = 6, and upsilon3 = 0, have been observed. Ab initio potential-energy surfaces for the X2B1 and A2A1 electronic states have been calculated at 210 points. These two states correlate with a 2Pi(u) state at linearity and they interact by the Renner-Teller coupling and spin-orbit coupling. Using the ab initio potential-energy surfaces with our RENNER computer program system, the vibronic structure and relative intensities of the A2A1 --> X2B1 emission band system have been calculated in order to corroborate the experimental assignments.     

F(2P)与CH2Br2反应的化学发光光谱及其动力学

This paper reported an observation of the chemiluminescence in the 400～900 nm spectral region produced by the crossed molecular beam reaction of F(~2P) with CH_2Br_2, as well as the reaction mechanism. Under single collision condition, only vibrationally excited HF~≠(X,V) (V≤3) can be observed. In the case of multicollision, in addition to V≤3, HF~≠(X,V) with V>3 and electronically excited Br_2~*(B), BrF~*(B) have been detected. The equilibrium rotational temperature for HF(3,0) band is 320 K, and the relative population ratio of different V levels of HF is N_3:N_4:N_5=0.69:1.00:0.12.     

氟原子与溴代甲烷反应化学发光研究

用光子计数技术系统地探测了F(^2P)原子与溴代甲烷等(CH~3Br、CH~2Br~2和CHBr~3)反应在各种压力下的可见区(300～900nm)化学发光,得到HF电子基态振动泛频跃迁及 Br~2(B)、BrF(B)、CHF(A)、CH(A) 等分子电子激发态跃迁的发射谱.求出HF(υ=3)转动温度为480K,计算机模拟光谱获得了Br~2(B)的振动布居.对比F与氯代甲烷反应的机理分析表明,初级反应主要是F提取形成HF,多级反应产生了电子激发态的产物分子.     

Deactivation of vibrationally excited hydrogen fluoride (v=2 and v=1) by atomic fluorine

Measurements have been made which provide information concerning the rate of energy transfer between vibrationally excited HF and atomic fluorine. It was found that HF (v = 1) deactivates about seven times slower than was determined in previous experiments. The deactivation rate constant for HF (v = 2) is about six times larger than for HF (v = 1).     

Direct detection of vibrational excitation in the CO2 product of the oxidation of CO on a platinum surface

Infrared chemliuminescence techniques are applied to the study of vibrationally excited surface reaction products. The method is demonstrated by the detection of infrared emission from highly excited CO₂ product molecules in the reaction of CO with O on a platinum surface.     

Infrared multiphoton dissociation of methyl nitrite

Methyl nitrite undergoes dissociation when irradiated with the focused output of a pulsed CO₂ TEA laser. Time resolved infrared emission is observed and attributed to vibrationally excited formaldehyde and methanol. These species are produced via reactions of methoxy radicals formed in the primary dissociation. Other products formed are NO and N₂O.     

Ultrafast fluorescence detection in tris(2,2'-bipyridine)ruthenium(II) complex in solution: relaxation dynamics involving higher excited states

The excited-state dynamics of a transition metal complex, tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)(3)](2+), has been investigated using femtosecond fluorescence upconversion spectroscopy. The relaxation dynamics in these molecules is of great importance in understanding the various ultrafast processes related to interfacial electron transfer, especially in semiconductor nanoparticles. Despite several experimental and theoretical efforts, direct observation of a Franck-Condon singlet excited state in this molecule was missing. In this study, emission from the Franck-Condon excited singlet state of [Ru(bpy)(3)](2+) has been observed for the first time, and its lifetime has been estimated to be 40 +/- 15 fs. Biexponential decays with a fast rise component observed at longer wavelengths indicated the existence of more than one emitting state in the system. From a detailed data analysis, it has been proposed that, on excitation at 410 nm, crossover from higher excited (1)(MLCT) states to the vibrationally hot triplet manifold occurs with an intersystem crossing time constant of 40 +/- 15 fs. Mixing of the higher levels in the triplet state with the singlet state due to strong spin-orbit coupling is proposed. This enhances the radiative rate constant, k(r), of the vibrationally hot states within the triplet manifold, facilitating the upconversion of the emitted photons. The vibrationally excited triplet, which is emissive, undergoes vibrational cooling with a decay time in the range of 0.56-1.3 ps and relaxes to the long-lived triplet state. The results on the relaxation dynamics of the higher excited states in [Ru(bpy)(3)](2+) are valuable in explaining the role of nonequilibrated higher excited sensitizer states of transition metal complexes in the electron injection and other ultrafast processes.     

Excited state properties of transition metal phosphine complexes

Phosphine ligands determine the excited state properties of a variety of coordination compounds. Phosphines not only influence metal-centered excited states, but participate directly in charge transfer transitions owing to their electron donating and accepting ability. Moreover, intraligand excited states are accessible if the phosphine carries suitable substituents. This diversity is illustrated by selected examples. The excited state behavior is discussed on the basis of spectral (absorption and emission) and photochemical properties of appropriate phosphine complexes.     

Quantum dynamics of vibration–vibration energy transfer for vibrationally excited HF colliding with H2

The rate constants for H₂–HF energy transfer processes, especially for those in vibrationally excited states, are very demanding in astrophysics and chemical laser engineering, especially for those in vibrationally excited states. Based on our recent potential energy surface, we used the coupled-states approximation including the nearest neighboring Coriolis couplings with energy-based local basis set to perform dynamics calculation for the H₂–HF energy transfer system. Rate constants for vibrational transitions (1; 3) → (0; 4), (1; 3) → (2; 2), and (0; 3) → (1; 2) were obtained. For state-to-state rate constants, transitions that have no internal angular momentum gap dominate at high temperatures. The vibrational-resolved rate constant for (1; 3) → (0; 4) initially decreases and then increases with the temperature, while those for (1; 3) → (2; 2), and (0; 3) → (1; 2) transitions monotonically increase. The calculated rate constants are in good agreement with the available experimental results. These dynamical data can be further applied to the numerical simulation of hydrogen fluoride chemical laser. © 2018 Wiley Periodicals, Inc.     

草酰氯和2,3-丁二酮的紫外光解

羰基化合物的光解一直是分子反应动力学研究感兴趣的课题之一,近年来许多研究小组用不同的实验方法对气相羰基化合物特别是丙酮分子的紫外光解进行了广泛的研究[14],然而对一个分子中含有两个羰基的二酮类分子却很少研究.早期对(ＣｌＣＯ)2和(ＣＨ3ＣＯ)2的光解反应研究主要集中在液相宏观动力学方面[5-7],这些研究都没有在分子的层次上进行考察,因此对它们的紫外光解机理并不清楚,例如两者光解首先发生的是Ｃｌ或ＣＨ3基的脱落,还是分子中央的Ｃ-Ｃ键断裂?光解后剩余的自由基第二步解离是光解还是热解?光解后碎片的能量分布如何?等等.为此…     

Intermolecular vibrations and dynamics of the anisole—benzene complex studied by multi-resonance spectroscopy

The intermolecular vibrations of the anisole—benzene complex in the ground and excited electronic states have been observed by the LIF (laser-induced fluorescence) and fluorescence-dip techniques. Short progressions due to the intermolecular vibrations suggest a small structure change of the complex upon electronic excitation. The LIF excitation spectrum shows predominant progressions of 27 cm⁻¹, which is tentatively assigned to one of the intermolecular bending modes in the excited electronic state. On the other hand, the fluorescence-dip spectrum shows only a series of bands with irregular intervals due to the intermolecular modes in the ground electronic state. The decay rates of the vibrationally excited complex in the ground electronic state have also been measured with the SEP-LIF (stimulated emission pumping-laser-induced fluorescence) technique, where the complex vibrationally excited by SEP is probed by the delayed LIF measurements. The complex excited to its purely intermolecular mode stays in the initially prepared state after a delay time of 1 μs. On the other hand, the complex excited to the intramolecular vibrational states above 500 cm⁻¹ does not seem to stay in the prepared states. Neither the relaxed complex nor the dissociated monomer was detected. A possible reason for this observation is discussed.