Vibrational energy transfer. Collisional quenching of competitive unimolecular reactions

1968 ◽  
Vol 46 (2) ◽  
pp. 341-343 ◽  
Author(s):  
D. C. Tardy ◽  
C. W. Larson ◽  
B. S. Rabinovitch
Keyword(s):  
Vibrational Energy ◽  
Heat Bath ◽  
Polyatomic Molecules ◽  
Unimolecular Reaction ◽  
Collisional Quenching ◽  
Kcal Mole ◽  
Vibrationally Excited ◽  
Reaction Systems ◽  
A Value ◽  
Collisional Deexcitation

A technique is described for the study of collisional deexcitation of highly vibrationally excited polyatomic molecules by use of externally activated competitive unimolecular reaction systems. This method has some advantages and is illustrated by the decomposition of chemically activated hexyl-3 radicals in the presence of H2 and CF4 as heat bath molecules. The former removes ~1.2 kcal mole−1 per successful collision; while for the latter a value in excess of 4.6 kcal is found so that CF4 behaves operationally like a strong collider.

The kinetics of elementary reactions involving the oxides of sulphur III. The chemiluminescent reaction between sulphur monoxide and ozone

1966 ◽  
Vol 295 (1443) ◽  
pp. 380-398 ◽  
Keyword(s):  
Ground State ◽  
Vibrational Energy ◽  
Excited Electronic State ◽  
Fluorescence Yield ◽  
Collisional Quenching ◽  
Kcal Mole ◽  
Elementary Reactions ◽  
Fluorescence Studies ◽  
Chemiluminescent Reaction ◽  
Electronically Excited

The chemiluminescent reaction between sulphur monoxide (SO) and ozone has been studied in a fast flow system at pressures between 0·3 and 3·0 mmHg, These species undergo a rapid bimolecular reation (1) SO + O 3 = SO 2 + O 2 + 106 kcal/mole (1) to yield ground state products, where k 1 = 1·5 x 10 12 exp ( –2100/ RT ) cm 3 mole -1 s -1 . This reaction also yields electronically excited SO 2 molecules in the 1 B and 3 B 1 states. The 1 B SO 2 molecules are produced with up to 16 kcal/mole vibrational energy. Emission from the longer lived 3 B 1 state is vibrationally relaxed and provides no information about the initial energy distribution. Comparison with fluorescence studies shows that the 3 B 1 SO 2 molecules are produced mainly by collisional quenching of SO 2 molecules formed in the 1 B state. The formation of electronically excited SO 2 is also a simple bimolecular process, but it involves a higher energy barrier than formation of ground state SO 2 . Our measurements on the chemiluminescence, when combined with data on the quenching of the SO 2 fluorescence, yield the rate constants k 1a = 10 11 exp ( – 4200/ RT ) and k lb ≯ 3 x 10 10 exp ( –3900/ RT ) cm 3 mole -1 s -1 for the bimolecular reactions SO + O 3 = SO 2 ( 1 B ) + O 2 + 21 kcal/mole, (1 a ) SO + O 3 = SO 2 ( 3 B 1 ) + O 2 + 35 kcal/mole (1 b ) which form electronically excited SO 2 . No electronically excited O 2 appears to be formed. It is deduced that electronically excited SO 2 is produced by crossing to a separate potential surface at or near the transition state rather than by the formation of a highly vibrationally excited SO 2 molecule which crosses to the excited electronic state.

State Preparation and Intramolecular Vibrational Energy Redistribution

1996 ◽  
Author(s):  
Tomas Baer ◽  
William L. Hase
Keyword(s):  
Vibrational Energy ◽  
Chemical Activation ◽  
Classical Trajectory ◽  
Unimolecular Reaction ◽  
Vibrationally Excited ◽  
Energy Redistribution ◽  
Rotational States ◽  
Intramolecular Vibrational Energy Redistribution ◽  
Singlet States ◽  
Reactant Molecule

The first step in a unimolecular reaction involves energizing the reactant molecule above its decomposition threshold. An accurate description of the ensuing unimolecular reaction requires an understanding of the state prepared by this energization process. In the first part of this chapter experimental procedures for energizing a reactant molecule are reviewed. This is followed by a description of the vibrational/rotational states prepared for both small and large molecules. For many experimental situations a superposition state is prepared, so that intramolecular vibrational energy redistribution (IVR) may occur (Parmenter, 1982). IVR is first discussed quantum mechanically from both time-dependent and time-independent perspectives. The chapter ends with a discussion of classical trajectory studies of IVR. A number of different experimental methods have been used to energize a unimolecular reactant. Energization can take place by transfer of energy in a bimolecular collision, as in . . . C2H6 + Ar → C2H6* + Ar . . . . . . (4.1) . . . Another method which involves molecular collisions is chemical activation. Here the excited unimolecular reactant is prepared by the potential energy released in a reactive collision such as . . . F + C2H4 → C2H4F* . . . . . . (4.2) . . . The excited C2H4F molecule can redissociate to the reactants F + C2H4 or form the new products H + C2H3F. Vibrationally excited molecules can also be prepared by absorption of electromagnetic radiation. A widely used method involves initial electronic excitation by absorption of one photon of visible or ultraviolet radiation. After this excitation, many molecules undergo rapid radiationless transitions (i.e., intersystem crossing or internal conversion) to the ground electronic state, which converts the energy of the absorbed photon into vibrational energy. Such an energization scheme is depicted in figure 4.1 for formaldehyde, where the complete excitation/decomposition mechanism is . . . H2CO(S0) + hν → H2CO(S1) → H2CO*(S0) → H2 + CO . . . . . . (4.3) . . . Here, S0 and S1 represent the ground and first excited singlet states.

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 .

The absorption spectrum of SO and the flash photolysis of sulphur dioxide and sulphur trioxide

1959 ◽  
Vol 249 (1259) ◽  
pp. 498-512 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Dissociation Energy ◽  
Sulphur Dioxide ◽  
Flash Photolysis ◽  
Ultra Violet ◽  
Vibrationally Excited ◽  
A Value ◽  
Continuous Absorption ◽  
Sulphur Trioxide ◽  
Normal Spectrum

The flash photolysis of sulphur dioxide under adiabatic conditions results in the complete temporary disappearance of its spectrum , which then slowly regains its original intensity over a period of several milliseconds. Simultaneously with the disappearance of the sulphur dioxide spectrum a continuous absorption appears in the far ultra-violet and fades slowly as the sulphur dioxide reappears. It is shown that the effect of the flash is thermal rather than photochemical, and the possibility of the existence of an isomer of sulphur dioxide at high temperatures is discussed; the disappearance of the normal spectrum on flashing is explained in this way. Several previously unrecorded bands of SO observed in the photolysis indicate that the vibrational numbering of its spectrum should be revised by the addition of 2 to the present values of v' . This leads to a value of the dissociation energy of 123.5 kcal. In formation about the levels v' = 4, 5 and 6 has also been obtained. The isothermal flash photolysis of sulphur trioxide results in the appearance of vibrationally excited SO, and the primary photochemical step in this reaction is discussed.

scholarly journals The calculation of TV, VT, VV, VV' − rate coefficients for the collisions of the main atmospheric components

1998 ◽  
Vol 16 (7) ◽  
pp. 838-846 ◽  
Author(s):  
A. S. Kirillov
Keyword(s):  
Experimental Data ◽  
Energy Transfer ◽  
Vibrational Energy ◽  
Relaxation Times ◽  
Atmospheric Composition ◽  
Rate Coefficients ◽  
Frequency Change ◽  
Vibrational Energy Transfer ◽  
Ion Chemistry ◽  
Vibrationally Excited

Abstract. The first-order perturbation approximation is applied to calculate the rate coefficients of vibrational energy transfer in collisions involving vibrationally excited molecules in the absence of non-adiabatic transitions. The factors of molecular attraction, oscillator frequency change, anharmonicity, 3-dimensionality and quasiclassical motion have been taken into account in the approximation. The analytical expressions presented have been normalized on experimental data of VT-relaxation times in N2 and O2 to obtain the steric factors and the extent of repulsive exchange potentials in collisions N2-N2 and O2-O2. The approach was applied to calculate the rate coefficients of vibrational-vibrational energy transfer in the collisions N2-N2, O2-O2 and N2-O2. It is shown that there is good agreement between our calculations and experimental data for all cases of energy transfer considered.Key words. Ionosphere (Auroral ionosphere; ion chemistry and composition). Atmospheric composition and structure (Aciglow and aurora).

THE REACTION OF METHYL RADICALS WITH FORMALDEHYDE

1959 ◽  
Vol 37 (9) ◽  
pp. 1462-1468 ◽  
Author(s):  
A. R. Blake ◽  
K. O. Kutschke
Keyword(s):  
Activation Energy ◽  
Kinetic Analysis ◽  
Addition Reactions ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
A Value ◽  
Abstraction Reaction ◽  
Butyl Peroxide

The pyrolysis of di-t-butyl peroxide has been reinvestigated and used as a source of methyl radicals to study the abstraction reaction between methyl radicals and formaldehyde. At low [HCHO]/[peroxide] ratios the system was simple enough for kinetic analysis, and a value of 6.6 kcal/mole was obtained for the activation energy. At higher [HCHO]/[peroxide] ratios the system became very complicated, possibly due to the increased importance of addition reactions.

Collisional quenching of molecular ro-vibrational energy by He buffer loading at ultralow energies

2006 ◽  
Vol 25 (3) ◽  
pp. 313-351 ◽  
Author(s):  
Enrico Bodo ◽  
Franco A. Gianturco
Keyword(s):  
Vibrational Energy ◽  
Collisional Quenching
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