The effect of CO rotation from shaped pulse polarization on reactions that form C2

2019 ◽  
Vol 21 (26) ◽  
pp. 14103-14110 ◽  
Author(s):  
Hannah M. Ogden ◽  
Tara J. Michael ◽  
Matthew J. Murray ◽  
Qingnan Liu ◽  
Carlos Toro ◽  
...  
Keyword(s):  
Rotational Energy ◽  
Bimolecular Reactions ◽  
Electronically Excited ◽  
Shaped Pulse ◽  
Pulse Polarization

The effect of CO rotational energy on bimolecular reactions to form electronically excited C2 is reported here.

Spectroscopic studies of low-pressure flames; temperature measurements in acetylene flames

1948 ◽  
Vol 194 (1037) ◽  
pp. 169-184 ◽  
Keyword(s):  
Reaction Zone ◽  
Rotational Temperature ◽  
Flame Temperature ◽  
Low Pressure ◽  
Spectroscopic Studies ◽  
Rotational Energy ◽  
Temperature Measurements ◽  
Oh Radicals ◽  
Electronically Excited ◽  
Combustion Processes

Flames at very low pressure haw a relatively thick reaction zone (or flame front) and are especially suitable for detailed study of the combustion processes and of the distribution of energy during the reaction. Temperature measurements have been made, by various spectroscopic methods, on flames of acetylene with air, oxygen and nitrous oxide, in some cases down to a pressure of 1.5 mm. Hg. The excitation temperature has been measured through the reaction zone by the spectrum-line reversal method using Fe, introduced as the carbonyl; the characteristics of the flame containing Fe(CO) 5 are described. The rotational temperature of the excited OH radicals has been determined from the emission spectrum; at pressures above 10 mm. it is fairly constant at around 5700° K, but at lower pressure rises to a higher value of nearly 9000° K. The results are explaihed in terms of the collision and radiative deactivation of the electronically excited OH radicals. These radicals are believed to be formed, as the result of chemical reaction, in the excited 2 Σ state and with a rotational energy equivalent to above 9000° K. Deactivation by collision appears to occur on the average after about forty collisions, if a normal collision diameter is assumed. Removal of electronic excitation occurs mainly by collisions with O 2 molecules, but CO 2 or CO molecules are most effective in removing rotational energy. The variation of concentration of OH through the reaction zone has been determined by its absorption spectrum; it is abnormally high just below the visible reaction zone. Calculations of flame temperature and composition are given. The lack of equipartition of energy is discussed.

Spectroscopic studies of low-pressure flames III. Effective rotational temperatures and excitation mechanism for C 2 bands

1950 ◽  
Vol 201 (1067) ◽  
pp. 561-569 ◽  
Keyword(s):  
Vibrational Energy ◽  
Low Pressure ◽  
Spectroscopic Studies ◽  
Rotational Energy ◽  
Excitation Mechanism ◽  
High Excitation ◽  
Excitation Process ◽  
Intensity Measurements ◽  
Electronically Excited

Intensity measurements on the Swan bands of C 2 give effective rotational temperatures for a number of flames. For oxygen/acetylene at 1 atm. the value is 4950° K, falling to 3800° K at 2 mm. For acetylene/air it is 3400° K at 1 atm., falling a little at low pressure. In discussing the excitation process, reasons are given against its being a true chemiluminescence. It is believed that the C 2 radicals are formed with high rotational energy and are electronically excited by collision with energy-rich molecules present in the flame and responsible for the high excitation temperatures previously recorded. These energy-rich molecules probably possess excess vibrational energy.

Energy distribution in electronically excited CH and C2 in low pressure hydrocarbon flames

1967 ◽  
Vol 45 (20) ◽  
pp. 2441-2449 ◽  
Author(s):  
Gaspar Ndaalio ◽  
Jacques M. Deckers
Keyword(s):  
Energy Distribution ◽  
Cross Section ◽  
Vibrational Energy ◽  
Low Pressure ◽  
Rotational Energy ◽  
Gas Mixture ◽  
Hydrocarbon Flames ◽  
Quantum Numbers ◽  
Electronically Excited ◽  
Vibrational Energy Distribution

A study has been made of the rotational energy distribution of electronically excited CH and of the vibrational energy distribution of electronically excited C2 radicals in low pressure (0.2 to 35 Torr) hydrocarbon flames. The rotational energy of the CH radical in the A2Δ (ν = 0) state has been found to be statistically distributed in the levels with quantum numbers 14 to 21. This distribution can be described by a temperature which has, however, no thermodynamic significance. In the methane–oxygen flame this temperature has been found to be independent of both the composition of the gas mixture and the pressure, whereas in the ethylene–oxygen system it varies with these parameters. Hydrogen–methane–oxygen flames behave as ethylene flames. Inert diluents such as nitrogen and carbon dioxide do not affect the temperature at very low pressures. This indicates that the energy distribution is not perturbed measurably by collisions before emission takes place. In order to explain these observations we have to accept that at least two reactions produce CH* in ethylene flames.The cross section for energy transfer out of the high rotational levels of CH(A2Δ) to flame gases is found to be smaller than 0.6 Å2 and that for transfer to CO2 is about 2 Å2.A statistical distribution also has been observed in the vibrational energy distribution of electronically excited C2. The corresponding temperature is about 6 500 °K and is independent of the composition of the gas mixture and of the fuel. It decreases very slowly with increasing pressure above 3 Torr. Inert diluents added to the gas mixture do not alter this temperature.The cross section for de-excitation of C2(A3πg) is found to be smaller than 2.5 Å2.

Dynamics of Ground State Bimolecular Reactions

1996 ◽  
Author(s):  
Curt Wittig ◽  
Ahmed H. Zewail
Keyword(s):  
Ground State ◽  
State Level ◽  
Chemical Transformations ◽  
Weakly Bound ◽  
Bimolecular Reactions ◽  
Weakly Bound Complexes ◽  
Electronically Excited ◽  
Gaseous Media ◽  
Chemical Selectivity ◽  
Elementary Chemical

During the past decade, the study of photoinitiated reactive and inelastic processes within weakly bound gaseous complexes has evolved into an active area of research in the field of chemical physics. Such specialized microscopic environments offer a number of unique opportunities which enable scientists to examine regiospecific interactions at a level of detail and precision that invites rigorous comparisons between experiment and theory. Specifically, many issues that lie at the heart of physical chemistry, such as reaction probabilities, chemical branching ratios, rates and dynamics of elementary chemical processes, curve crossings, caging, recombination, vibrational redistribution and predissociation, etc., can be studied at the state-to-state level and in real time. Inevitably, understanding the photophysics and photochemistry of weakly bound complexes lends insight into corresponding processes in less rarefied surroundings, for example, molecules physisorbed on crystalline insulator and metal surfaces, molecules residing on the surfaces of various ices, and molecules weakly solvated in liquids. However, such ties to the real world are not the main driving force behind studies of photoinitiated reactions in complexed gaseous media. Rather, it is the lure of going a step beyond the more common molecular environments. Theoretical modeling, which in many areas purports to challenge experiment, must rise to the occasion here if it is to offer predictive capability for even the simplest of such microcosms. Subtleties abound. Roughly speaking, two disparate regimes can be identified which are accessible experimentally and which correspond to qualitatively different kinds of chemical transformations. These are distinguished by their reactants: electronically excited versus ground state. For example, it is possible to study the chemical selectivity that derives from the alignment and orientation of excited electronic orbitals, albeit at restricted sets of nuclear coordinates. This is achieved by electronically exciting a complexed moiety, such as a metal atom, which then undergoes chemical transformations that depend on the geometric properties of the electronic orbitals such as their alignments and orientations relative to the other moiety (or moieties) in the complex.

Carbon-Heteroatom Cross-Coupling via an Electronically Excited Nickel (II) Complex

2019 ◽  
Author(s):  
Randolph Escobar ◽  
Jeffrey Johannes
Keyword(s):  
Energy Transfer ◽  
Functional Groups ◽  
Cross Coupling ◽  
Reductive Elimination ◽  
Aryl Halides ◽  
Coupling Reactions ◽  
General Methodology ◽  
Cross Coupling Reactions ◽  
Electronically Excited ◽  
Energy Transfer Pathway

<div>While carbon-heteroatom cross coupling reactions have been extensively studied, many methods are specific and</div><div>limited to a set of substrates or functional groups. Reported here is a method that allows for C-O, C-N and C-S cross coupling reactions under one general methodology. We propose that an energy transfer pathway, in which an iridium photosensitizer produces an excited nickel (II) complex, is responsible for the key reductive elimination step that couples aryl halides to 1° and 2° alcohols, anilines, thiophenols, carbamates and sulfonamides.</div>

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