MULTISTAGE DEACTIVATION IN THE PHOTOLYSIS OF HEXAFLUOROACETONE

1964 ◽  
Vol 42 (6) ◽  
pp. 1345-1354 ◽  
Author(s):  
A. N. Strachan ◽  
R. K. Boyd ◽  
K. O. Kutschke
Keyword(s):  
Vibrational Energy ◽  
Excited Molecule ◽  
Single Step ◽  
Inert Gases ◽  
Ultraviolet Region ◽  
Vibrationally Excited ◽  
Vibrational Levels ◽  
New Treatments ◽  
Lower Group ◽  
Vibrational Equilibrium

In principle the vibrationally excited molecule in an upper electronic state, formed by absorption in the ultraviolet region of the spectrum, can attain vibrational equilibrium by two mechanisms. In most discussions of this degradation of vibrational energy it has been considered that the data are represented adequately by a single-step deactivation from high to low vibrational levels rather than by a multistep cascade from one group of vibrational levels to the next lower group. The present work suggests new treatments of the experimental data by which it is possible to distinguish between the single- and the multi-step deactivation processes. It is demonstrated that the literature data on the quantum yield for the decomposition of hexafluoroacetone is better interpreted in terms of a multistep deactivation. Some new data are presented which support this conclusion.Methods to evaluate the efficiencies as deactivating agents of added inert gases are discussed. It is suggested that the deactivation of excited hexafluoroacetone by hydrocarbons might involve chemical rather than, or in addition to, purely physical quenching.

Vibrational energy distribution in HF formed by elimination from activated CH3CF3 and CH2CF2

1970 ◽  
Vol 48 (18) ◽  
pp. 2919-2930 ◽  
Author(s):  
P. N. Clough ◽  
J. C. Polanyi ◽  
R. T. Taguchi
Keyword(s):  
Rate Constants ◽  
Vibrational Energy ◽  
Flow System ◽  
Relative Rate ◽  
Elimination Reaction ◽  
Vibrationally Excited ◽  
Vibrational Levels ◽  
Relative Rate Constants ◽  
Fast Flow ◽  
Vibrational Energy Distribution

The combination–elimination reaction CH3 + CF3 → CH3CF3† → CH2CF2 + HF has been studied in a fast-flow system. Infrared chemiluminescence arising from the HF product has been observed from vibrational levels v = 1–4, and relative rate constants, k(v), have been obtained for HF formation in these levels. A study has also been made of the reaction CH2CF2 + Hg*(63P1) → CHCF + HF + Hg(61S0), which has been found to produce vibrationally-excited HF. Relative rate constants k(v) for vibrational levels v = 1–4 have been obtained. It appears that channelling of the potential energy into HF vibration, in the course of the elimination step, is more efficient in the first than in the second of these reactions. In the second reaction HF is eliminated with considerable rotational excitation.

Evolution of the homogeneous IR spectrum of a highly vibrationally excited molecule as a result of a change in its vibrational energy

1988 ◽  
Vol 47 (3) ◽  
pp. 229-232 ◽  
Author(s):  
S. I. Ionov ◽  
A. A. Stuchebryukhov ◽  
V. N. Bagratashvili ◽  
V. N. Lokhman ◽  
G. N. Makarov ◽  
...  
Keyword(s):  
Ir Spectrum ◽  
Vibrational Energy ◽  
Excited Molecule ◽  
Vibrationally Excited

FLUORESCENCE EFFICIENCY OF CYCLOPENTANONE VAPOR AND ITS RELATION TO PHOTOLYSIS

1963 ◽  
Vol 41 (2) ◽  
pp. 287-292 ◽  
Author(s):  
S. R. La Paglia ◽  
B. C. Roquitte
Keyword(s):  
Fluorescence Spectrum ◽  
High Pressures ◽  
Vibrational Energy ◽  
Energy Content ◽  
Excited Molecule ◽  
Inert Gases ◽  
Fluorescence Efficiency ◽  
Liquid Solutions ◽  
Temperature And Pressure ◽  
First Time

Cyclopentanone vapor, when excited by light of wavelength 3130 Å, gives rise to four different photoproducts and fluorescence. The photochemistry of the molecule has been investigated by Srinivasan (J. Am. Chem. Soc. 81, 1546 (1959); 83, 4344, 4348 (1961)). In the present work the fluorescence spectrum and fluorescence efficiency of cyclopentanone vapor are reported for the first time. The fluorescence spectrum is identical with that obtained from liquid solutions of cyclopentanone, with a maximum at 4100 Å. Time, temperature, oxygen, and inert gases do not affect the spectrum, which contains no component ascribable to phosphorescence, maximum 4450 Å. Beer's law is obeyed.The fluorescence efficiency is also found to be independent of the variables temperature and pressure of inert gas, cyclopentanone, and oxygen. This is in marked contrast with the behavior of the photochemical yields (see work by Srinivasan). The yields of cyclobutane and ethylene tend to increase at high vibrational energy content of the excited molecule (low pressure, high temperature, short exciting wavelengths), while the yield of pentenal increases under conditions of decreasing vibrational energy content (high pressures, etc.). The fact that fluorescence stabilization does not occur in cyclopentanone can be related to the results of photolysis.

Laser-excited fluorescence of 15NO2 and N18O2

1976 ◽  
Vol 54 (10) ◽  
pp. 1069-1076 ◽  
Author(s):  
J. C. D. Brand ◽  
J. L. Hardwick ◽  
K. E. Teo
Keyword(s):  
Ground State ◽  
Selection Rule ◽  
Vibrational Energy ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Resonance Fluorescence ◽  
Vibrationally Excited ◽  
Vibrational Levels ◽  
Vibrational Constants ◽  
Electronic Ground

Measurements are reported of the resonance fluorescence of 15N16O2 and 14N18O2 excited by the 488,496, and 514 nm radiation of an Ar+ laser. The frequency displacements in these spectra are consistent with values calculated previously, using potential constants for the electronic ground state of NO2 derived from the rotational and vibrational constants of NO2 and 15N16O2 but containing no information from N18O2 spectra; the agreement obtained for the latter isotope is therefore a partial test of the potential field.In these spectra, fluorescence occurs from vibronic B2 levels of the Ã2B2 state possessing 7500–8500 cm−1 of vibrational energy. A number of examples are described in which the emission from these vibrationally excited levels shows an anomalous intensity distribution or K-selection rule (e.g., ΔK = ±2) as a result of Coriolis and/or spin–orbit coupling between vibrational levels of the upper electronic state.

The study of energy transfer by kinetic spectroscopy I. The production of vibrationally excited oxygen

1956 ◽  
Vol 233 (1195) ◽  
pp. 455-464 ◽  
Keyword(s):  
Flash Photolysis ◽  
Vibrational Energy ◽  
Vibrationally Excited ◽  
Near Resonance ◽  
Vibrational Levels ◽  
Great Excess ◽  
First Time ◽  
Kinetics Of ◽  
Excited Oxygen ◽  
Electronic Ground

The flash photolysis of chlorine dioxide or of nitrogen dioxide in a great excess of inert gasyields oxygen molecules in their electronic ground states with up to eight quanta of vibrational energy. By a study of the reaction kinetics of the two systems, it is concluded that these excited molecules have their origin in the reactions O + NO 2 = NO + O 2 and O + CIO 2 = CIO + O 2 respectively. Thus, for the first time we have available a very convenient method of studying the collisional transfer and degradation of vibrational energy from molecules in the higher vibrational levels of the ground state and some preliminary measurements of the efficiency of deactivation by various molecules are given. It is concluded that the energy is removed most readily either when there is near resonance of the vibrational levels with those of the oxygen, or by free radicals. Some of the reactions of the chlorine oxides present are also discussed.

The flash photolysis of ozone

1957 ◽  
Vol 242 (1230) ◽  
pp. 265-276 ◽  
Keyword(s):  
Electronic State ◽  
Vibrational Energy ◽  
Inert Gases ◽  
Inert Gas ◽  
Ground Electronic State ◽  
Explosive Decomposition ◽  
Kcal Mole ◽  
Vibrationally Excited ◽  
Energy Chain ◽  
Excited Oxygen

The photolytic decomposition of ozone in ultra-violet radiation has been studied by kinetic spectroscopy. It has been shown that vibrationally excited oxygen in its ground electronic state plays a most important part in the decomposition. These molecules have sufficient vibrational energy to bring about dissociation of ozone, thus regenerating oxygen atoms which can again produce vibrationally excited oxygen. The importance of this energy chain is emphasized by comparative studies on the explosive decomposition of pure ozone, and the isothermal decomposition when an excess of inert gas is present. In the former case the O* 2 is removed so rapidly, mainly by reaction with ozone, that no absorption due to it can be detected. Using an excess of inert gas to obtain isothermal conditions it has been possible to observe Schumann–Runge absorption of oxygen molecules in their ground electronic state, with up to 16 quanta of vibrational energy. The vibrational energy distribution of the oxygen molecules formed has an apparent maximum at v " = 13 (53.5 kcal/mole) and falls off sharply at v " = 12 and 16 (49.0 and 63.2 kcal/mole). It is shown that the only reasonable reaction for the production of excited oxygen is O + O 3 → O* 2 + O 2 . Studies on the rate of ozone decay with time have also been carried out and the results analyzed in terms of the rate constants of reactions involving the deactivation of excited oxygen and the three-body recombination O + O 2 + M → O 3 + M . It is shown that the spherically symmetrical and chemically inert gases such as A, He and SF 6 are much less efficient in bringing about recombination than N 2 , N 2 O or CO 2 .

Two-Dimensional Infrared Spectroscopy From the Gas to Liquid Phase: Density Dependent J-Scrambling, Vibrational Relaxation, and the Onset of Liquid Character

2019 ◽  
Author(s):  
Greg Ng Pack ◽  
Matthew Rotondaro ◽  
Parth Shah ◽  
Aritra Mandal ◽  
Shyamsunder Erramilli ◽  
...  
Keyword(s):  
Vibrational Energy ◽  
Rotational Relaxation ◽  
Vibrational Energy Relaxation ◽  
Pump Probe ◽  
Solution Dynamics ◽  
Supercritical Phase ◽  
Supercritical Solution ◽  
Asymmetric Stretch ◽  
Two Dimensional Infrared Spectroscopy ◽  
Vibrational Equilibrium

Ultrafast 2DIR spectra and pump-probe responses of the N2O n 3 asymmetric stretch in SF6 as a function of density from the gas to supercritical phase and liquid are reported. 2DIR spectra unequivocally reveal free rotor character at all densities studied in the gas and supercritical region. Analysis of the 2DIR spectra determines that J-scrambling or rotational relaxation in N2O is highly efficient, occurring in ~1.5 to ~2 collisions with SF6 at all non-liquid densities. In contrast, N2O n 3 vibrational energy relaxation requires ~15 collisions, and complete vibrational equilibrium occurs on the ~ns scale at all densities. An independent binary collision model is sufficient to describe these supercritical state point dynamics. The N2O n 3 in liquid SF6 2DIR spectrum shows no evidence of free rotor character or spectral diffusion. Using these 2DIR results, hindered rotor or liquid-like character is found in gas and all supercritical solutions for SF6 densities ³ r * = 0.3, and increases with SF6 density. 2DIR spectral analysis offers direct time domain evidence of critical slowing for SF6 solutions closest to the critical point density. Applications of 2DIR to other high density and supercritical solution dynamics and descriptions are discussed. <br>

Molecules in strong laser fields: vibrational inversion and harmonic generation

1994 ◽  
Vol 72 (3) ◽  
pp. 673-677 ◽  
Author(s):  
Eric E. Aubanel ◽  
André D. Bandrauk
Keyword(s):  
Harmonic Generation ◽  
Laser Pulses ◽  
Harmonic Spectrum ◽  
Femtosecond Laser Pulses ◽  
Generation Process ◽  
High Order Harmonic Generation ◽  
Vibrationally Excited ◽  
Potential Wells ◽  
High Order Harmonic ◽  
Vibrational Levels

We examine two consequences of the unique behaviour of molecules in strong fields. First, by time gating of laser-induced avoided crossings with femtosecond laser pulses, one can obtain efficient vibrational inversion into a narrow distribution of vibrational levels of a molecular ion. We demonstrate this by numerical solution of the time-dependent Schrödinger equation for [Formula: see text] Second, we show results of numerical calculation with vibrationally excited [Formula: see text] of harmonic generation up to the 11th order of an intense 1064- nm laser. We predict that competition of photodissociation can be minimized by trapping the molecule in high-field-induced potential wells, thus enhancing the high-order harmonic generation process. Furthermore, the harmonic spectrum can serve as a measure of the structure of these laser-induced potentials.

The microwave spectrum of the OH X2Π radical in the ground and vibrationally-excited (ν ≤ 6) levels

1979 ◽  
Vol 57 (5) ◽  
pp. 619-634 ◽  
Author(s):  
J. A. Coxon ◽  
K. V. L. N. Sastry ◽  
J. A. Austin ◽  
D. H. Levy
Keyword(s):  
Absorption Spectrum ◽  
Parallel Plate ◽  
Microwave Spectrum ◽  
Hamiltonian Matrix ◽  
Centrifugal Distortion ◽  
Linear Least Squares ◽  
Vibrationally Excited ◽  
Hyperfine Constants ◽  
Vibrational Levels ◽  
Astrophysical Significance

The microwave absorption spectrum of the OH X2Π radical has been observed in all vibrational levels up to ν = 6. Experimental details are described of the tunable cavity and parallel plate Stark-modulated spectrometers employed for transitions below and above 23 GHz, respectively. The observed line frequencies, together with those reported by other workers, have been fitted using a non-linear least-squares routine with numerical diagonalization of the Hamiltonian matrix. Pseudo high-order corrections for centrifugal distortion of the Λ-doubling are required for the ν = 0 data, which now extend to J = 19/2 in the 2Π1/2 component. The various adjustable parameters of the Hamiltonian are compared with those of other similar models. The Λ-doubling and magnetic hyperfine constants for the different vibrational levels are reported, and several line frequencies of potential astrophysical significance are predicted.

scholarly journals Subauroral red arcs as a conjugate phenomenon: comparison of OV1-10 satellite data with numerical calculations

1997 ◽  
Vol 15 (8) ◽  
pp. 984-998 ◽  
Author(s):  
A. V. Pavlov
Keyword(s):  
Electron Density ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Atomic Oxygen ◽  
Major Ions ◽  
Integral Intensity ◽  
Rate Coefficients ◽  
Vibrationally Excited ◽  
Vibrational Distribution ◽  
Vibrational Levels

Abstract. This study compares the OV1-10 satellite measurements of the integral airglow intensities at 630 nm in the SAR arc regions observed in the northern and southern hemisphere as a conjugate phenomenon, with the model results obtained using the time-dependent one-dimensional mathematical model of the Earth ionosphere and plasmasphere (the IZMIRAN model) during the geomagnetic storm of the period 15–17 February 1967. The major enhancements to the IZMIRAN model developed in this study are the inclusion of He+ ions (three major ions: O+, H+, and He+, and three ion temperatures), the updated photochemistry and energy balance equations for ions and electrons, the diffusion of NO+ and O2+ ions and O(1D) and the revised electron cooling rates arising from their collisions with unexcited N2, O2 molecules and N2 molecules at the first vibrational level. The updated model includes the option to use the models of the Boltzmann or non-Boltzmann distributions of vibrationally excited molecular nitrogen. Deviations from the Boltzmann distribution for the first five vibrational levels of N2 were calculated. The calculated distribution is highly non-Boltzmann at vibrational levels v > 2 and leads to a decrease in the calculated electron density and integral intensity at 630 nm in the northern and southern hemispheres in comparison with the electron density and integral intensity calculated using the Boltzmann vibrational distribution of N2. It is found that the intensity at 630 nm is very sensitive to the oxygen number densities. Good agreement between the modelled and measured intensities is obtained provided that at all altitudes of the southern hemisphere a reduction of about factor 1.35 in MSIS-86 atomic oxygen densities is included in the IZMIRAN model with the non-Boltzmann vibrational distribution of N2. The effect of using of the O(1D) diffusion results in the decrease of 4–6% in the calculated integral intensity of the northern hemisphere and 7–13% in the calculated integral intensity of the southern hemisphere. It is found that the modelled intensities of the southern hemisphere are more sensitive to the assumed values of the rate coefficients of O+(4S) ions with the vibrationally excited nitrogen molecules and quenching of O+(2D) by atomic oxygen than the modelled intensities of the northern hemisphere.

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