Total Removal Rate Constants Research Articles

Doppler-Resolved Kinetics of Saturation Recovery.

Frequency-modulated laser transient absorption has been used to monitor the ground-state rotational energy-transfer rates of CN radicals in a double-resonance, depletion recovery experiment. When a pulsed laser is used to burn a hole in the equilibrium ground-state population of one rotational state without velocity selection, the population recovery rate is found to depend strongly on the Doppler detuning of a narrow-band probe laser. Similar effects should be apparent for any relaxation rate process that competes effectively with velocity randomization. Alternative methods of extracting thermal rate constants in the presence of these non-thermal conditions are evaluated. Total recovery rate constants, analogous to total removal rate constants in an experiment preparing a single initial rotational level, are in good agreement with quantum scattering calculations, but are slower than previously reported experiments and show qualitatively different rotational state dependence between Ar and He collision partners. Quasi-classical trajectory studies confirm that the differing rotational state dependence is primarily a kinematic effect.

Theoretical investigation of rotationally inelastic collisions of CH2(${\tilde{X}}$X̃) with helium

Following our earlier work on collisions of He with the methylene radical in its excited ã(1)A(1) state [L. Ma, M. H. Alexander, and P. J. Dagdigian, J. Chem. Phys. 134, 154307 (2011)], we investigate here the analogous relaxation of CH(2) in its ground X(3)B(1) electronic state. The molecule is treated as semi-rigid, with fixed bond lengths but a varying bond angle. We use an ab initio potential energy surface (PES) which is averaged over the CH(2) bending angle weighted by the square of the bending wave function. The PES for the interaction of He with CH(2) in the X state is considerably less anisotropic than for interaction with the ã state since the two 2p electrons on the C atom are evenly distributed among the bonding and non-bonding molecular orbitals. We report quantum scattering calculations of state-to-state and total removal cross sections as well as total removal rate constants at room temperature. Because of the less pronounced anisotropy, these cross sections and rate constants are considerably smaller than for collisions of CH(2)(ã) with He. Finally, we investigate the dependence of rotational inelasticity on the bending vibrational quantum number.

Rotational and vibrational energy transfer in vibrationally excited acetylene at energies near 6560 cm−1

Collisional energy transfer kinetics of vibrationally excited acetylene has been examined for states with internal energies near 6560 cm(-1). Total population removal rate constants were determined for selected rotational levels of the (1,0,1,0(0),0(0)) and (0,1,1,2(0),0(0)) states. Values in the range of (10-18) × 10(-10) cm(3) s(-1) were obtained. Measurements of state-to-state rotational energy transfer rate constants were also carried out for these states. The rotational energy transfer kinetics was found to be consistent with simple energy gap models for the transfer probabilities. Vibrational transfer out of the (0,1,1,2(0),0(0)) state accounted for no more than 16% of the total removal process. Transfer from (1,0,1,0(0),0(0)) to the u-symmetry (0,2,0,3(1),1(-1)), (0,1,1,2(0),0(0)), and (1,1,0,1(1),1(-1)) states was observed. Applying the principle of detailed balance to these data indicated that vibrational transfer to (1,0,1,0(0),0(0)) accounted for ~0.1% of the population loss from (0,2,0,3(1),1(-1)) or (0,1,1,2(0),0(0)), and 3% of the loss from (1,1,0,1(1),1(-1)). Relative rotational transfer probabilities were obtained for transfer to the g-symmetry (1,1,0,2(0),0(0))∕(0,0,2,0(0),0(0)) dyad. These results are related to recent studies of optically pumped acetylene lasers.

Collisional removal of OH(X2Π,υ= 9) by O, O2, O3, N2, and CO2

[1] Total removal rate constants of OH(υ = 9) by O atoms, O2, O3, N2, and CO2 were measured at room temperature. Ozone photodissociation at 248 nm in a mixture containing H2 generates O atoms and OH(υ = 9) by the secondary reaction of H atoms with excess O3. Steady state OH(υ = 9) population measurements using laser-induced fluorescence (LIF) determine the relative rate constants for OH(υ = 9) removal by other species present in the gas mixture. Using available measurements of the absolute removal rate constants by O3 and CO2, we extract a value of (4 ± 1) × 10−10 cm3s−1 (2σ) for the OH(υ = 9) + O rate constant. Collisional removal by O2 and N2 is approximately 20 and 600 times slower, respectively. The result for OH(υ = 9) + O indicates that fast O-atom processes play an important role in determining the OH emission and chemical heating rates in the middle terrestrial atmosphere.

Theoretical investigation of rotationally inelastic collisions of the methyl radical with helium

Rotationally inelastic collisions of the CH(3) molecule in its ground X(2)A(2)'' electronic state have been investigated. We have determined a potential energy surface (PES) for the interaction of rigid CH(3), frozen at its equilibrium geometry, with a helium atom, using a coupled-cluster method that includes all single and double excitations, as well as perturbative contributions of connected triple excitations [RCCSD(T)]. The anisotropy of the PES is dominated by repulsion of the helium by the hydrogen atoms. The dissociation energy D(e) was computed to equal 27.0 cm(-1). At the global minimum, the helium atom lies in the CH(3) plane between two C-H bonds at an atom-molecule separation R = 6.52 bohr. Cross sections for collision-induced rotational transitions have been determined through quantum scattering calculations for both nuclear spin modifications. Rotationally inelastic collisions can cause a change in the rotational angular momentum n and its body-frame projection k. Because of the anisotropy of the PES due to the hydrogen atoms, there is a strong propensity for Δk = ±3 transitions. Thermal rate constants for state-specific total collisional removal have also been determined.

Theoretical investigation of rotationally inelastic collisions of CH2(ã) with helium

Rotationally inelastic collisions of the CH(2) molecule in its ã(1)A(1) electronic state have been investigated. We have determined a potential energy surface (PES) for the interaction of rigid CH(2)(ã), frozen at its equilibrium geometry, with a helium atom, using a coupled-cluster method that includes all single and double excitations, as well as perturbative contributions of connected triple excitations [RSSCD(T)]. The PES is quite anisotropic, due to lack of electron density in the unoccupied CH(2) non-bonding orbital perpendicular to the molecular plane. Quantum scattering calculations have been carried out to compute state-to-state rotational energy transfer and elastic depolarization cross sections at collision energies up to 2400 cm(-1). These cross sections were thermally averaged to derive room-temperature rate constants. The total removal and elastic depolarization rate constants for the ortho k(a) = 1 levels agree well with recent experimental measurements by Hall, Sears, and their co-workers. We observe a strong even-odd alternation in the magnitude of the total rate constants which we attribute to the asymmetry splitting of the k(a) = 1 levels.

Experimental and Theoretical Investigations of Rotational Energy Transfer in HBr + He Collisions

Rotational relaxation rates for HBr(v = 1) colliding with helium atoms at room temperature have been measured using a time-resolved optical-optical double resonance technique. Rotational state selective excitation of v = 1 for rotational levels in the range J = 1-9 was achieved by stimulated Raman pumping. The population decay in the prepared states and the transfer of population to nearby rotational states was monitored via 2 + 1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy using the g(3)Σ(-)-X(1)Σ(+) (0-1) band. Collision-induced population evolution for transfer events with |ΔJ| ≤ 8 was observed at pressures near 0.7 Torr. The experimental data were analyzed using fitting and scaling functions to generate state-to-state rotational energy transfer rate constant matrices. Total depopulation rate constants were found to be in the range (1.3 to 2.0) × 10(-10) cm(3) s(-1). As a test of current computational methods, state-to-state rotational energy transfer rate constants were calculated using ab initio theory. The total removal rate constants were in good agreement with the measured values, but the transfer probabilities for events with |ΔJ| ≥ 3 were underestimated. Inspection of the anisotropic characteristics of the potential energy surface did not yield an obvious explanation for the discrepancies, but it is most likely that the problem stems from inaccuracies in the potential surface.

Elastic depolarization and polarization transfer in CN(A2Π, v = 4)+Ar collisions

Rate constants for collisional loss and transfer of population and rotational angular momentum alignment have been determined for the CN(A2Π, v = 4)+Ar system. Aligned samples of CN(A2Π, v = 4, F 1, j = 1.5–23.5e) were prepared by optical pumping on the A–X(4,0) band. Their evolution was observed using Doppler-resolved frequency-modulated spectroscopy in stimulated emission on the A–X(4,2) band. State-resolved total population removal rate constants, and state-to-state rotational energy transfer (RET) rate constants, are found to be in excellent agreement with previous experimental measurements and theoretical predictions for the v = 3 level. Rapid elastic depolarization of rotational alignment was observed for j = 1.5–6.5, with an average rate constant of 1.1 × 10−10 cm3 s−1. This declines with increasing j, reaching zero within experimental error for j = 23.5. The polarization transfer efficiency of the initially created alignment in state-to-state RET was also determined for the selected initial state j = 6.5, F 1, e. Substantial depolarization of the alignment was observed for small Δj transitions. Alignment transfer efficiencies ranged from 0.55 ± 0.06 for Δj = −1, to 0.32 ± 0.08 for Δj = +3. These measurements are discussed with reference to recent experimental and theoretical advances on collisional depolarization of related open-shell species. We suggest that the surprisingly efficient collisional depolarization observed may be the result of the multiple potential energy surfaces involved in this system.

Rotationally Inelastic Collisions of CN(A2Π) with Small Molecules

An optical-optical double resonance technique has been utilized to investigate rotational energy transfer of selected rotational/fine-structure levels of CN(A(2)Pi, v = 3) in collisions with the molecular partners CO(2) and CH(4). Total removal rate constants for several rotational/fine-structure levels were measured for both collision partners. State-to-state relative rate constants were determined for several initial levels. These show a strikingly strong collisional propensity to conserve the fine-structure/Lambda-doublet label, akin to our previous observations with the N(2) collision partner. The possible origin of this propensity is discussed.

Experimental and Theoretical Study of Rotationally Inelastic Collisions of CN(A2Π) with N2

Optical-optical double resonance was employed to study rotational energy transfer in collisions of selected rotational/fine-structure levels of CN(A2pi, v = 3) with N2. The CN radical was generated by 193 nm photolysis of BrCN in a slow flow of N2 at total pressures of 0.2-1.4 Torr. Specific fine-structure lambda-doublet levels of CN(A2pi, v = 3) were prepared by pulsed dye laser excitation on isolated lines in the CN A-X (3,0) band, while the initially excited and collisionally populated levels were observed after a short delay by laser-induced fluorescence in the B-A (3,3) band. Total removal rate constants for specified rotational/fine-structure levels involving total angular momentum J from 4.5 to 12.5 were determined. These rate constants decrease with increasing J, with no obvious dependence on the fine-structure/lambda-doublet label. State-to-state relative rate constants were determined for several initial levels and show a strikingly strong collisional propensity to conserve the fine-structure/lambda-doublet label. Comparison is made with the results of quantum scattering calculations based on potential energy surfaces averaged over the orientation of the N2 molecule. Reasonable agreement is found with experimentally determined total removal rate constants. However, the computed state-to-state rate constants show a stronger propensity for fine-structure and lambda-doublet changing transitions. These differences between experiment and theory could be due to the neglect of the N2 orientation and the correlation of the CN and N2 angular motions.

Inelastic scattering of OH(X 2Π) with Ar and He: a combined polarization spectroscopy and quantum scattering study

One-colour polarization spectroscopy (PS) on the OH A (2)Sigma(+)- X (2)Pi(0,0) band has been used to measure the removal of bulk rotational angular momentum alignment of ground-state OH(X (2)Pi) in collisions with He and Ar. Pseudo-first-order PS signal decays at different collider partial pressures were used to determine second-order decay rate constants for the X (2)Pi(3/2), J = 1.5-6.5, e states. The PS signal decay rate constant, k(PS), is sensitive to all processes that remove population and destroy polarization. The contribution to k(PS) from pure (elastic) alignment depolarization within the initial level, k(DEP), can be extracted by subtracting the independently measured or predicted sum of the rate constants for total rotational energy transfer (RET), k(RET), and for Lambda-doublet changing, k(Lambda), collisions from k(PS). Literature values of k(RET) and k(Lambda) are available from experiments with He and Ar, and from quantum scattering calculations for Ar only. We therefore also present the results of new, exact, fully quantum mechanical calculations of k(RET) and k(Lambda) on the most recent ab initio OH(X)-He potential energy surface of Lee et al. [J. Chem. Phys. 2000, 113, 5736]. The results for k(DEP) from this subtraction for He are found to be modest, around 0.4 x 10(-10) cm(3) s(-1), whereas for Ar k(DEP) is found to range between 0.6 +/- 0.2 x 10(-10) cm(3) s(-1) and 1.7 +/- 0.3 x 10(-10) cm(3) s(-1), comparable to total population removal rate constants. The differences between k(DEP) for the two colliders are most likely explained by the presence of a substantially deeper attractive well for Ar than for He. The measurement of k(DEP) may provide a useful new tool that is more sensitive to the form of the long-range part of the intermolecular potential than rotational state-changing collisions.

Kinetics of the Reactions of Cl*(2P1/2) and Cl(2P3/2) Atoms with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH at 295 K

The title reactions were studied using laser flash photolysis/laser-induced-fluorescence (FP-LIF) techniques. The two spin-orbit states, Cl*(2P(1/2)) and Cl(2P(3/2)), were detected using LIF at 135.2 and 134.7 nm, respectively. Measured reaction rate constants were as follows (units of cm3 molecule(-1) s(-1)): k(Cl(2P(3/2))+CH3OH) = (5.35 +/- 0.24) x 10(-11), k(Cl(2P(3/2))+C2H5OH) = (9.50 +/- 0.85) x 10(-11), k(Cl(2P(3/2))+n-C3H7OH) = (1.71 +/- 0.11) x 10(-10), and k(Cl(2P(3/2))+i-C3H7OH) = (9.11 +/- 0.60) x 10(-11). Measured rate constants for total removal of Cl*(2P(1/2)) in collisions with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH were (1.95 +/- 0.13) x 10(-10), (2.48 +/- 0.18) x 10(-10), (3.13 +/- 0.18) x 10(-10), and (2.84 +/- 0.16) x 10(-10), respectively; quoted errors are two-standard deviations. Although spin-orbit excited Cl*(2P(1/2)) atoms have 2.52 kcal/mol more energy than Cl(2P(3/2)), the rates of chemical reaction of Cl*(2P(1/2)) with CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH are only 60-90% of the corresponding Cl(2P(3/2)) atom reactions. Under ambient conditions spin-orbit excited Cl* atoms are responsible for 0.5%, 0.5%, 0.4%, and 0.7% of the observed reactivity of thermalized Cl atoms toward CH3OH, C2H5OH, n-C3H7OH, and i-C3H7OH, respectively.

State-to-state rate constants for collision induced energy transfer of electronically excited NH2 with NH3

Collisional energy transfer of NH2 in its electronically excited state à 2A1 is investigated with time-resolved Fourier transform emission spectroscopy. NH2 is produced by photodissociation of NH3 and relaxed to low rotational levels before excitation into the electronically excited state. Originating from collisions with NH3, rate constants for total collisional removal and state-to-state rate constants for rotational energy transfer within v2=4, Ka=1 with collision induced changes of |ΔKc|⩽3 are determined. The latter rate constants are fitted with several scaling laws. Among these, those based on the energy corrected sudden approximation work best. An approximate potential curve for the anisotropic part of the interaction potential is derived and verified with cross sections obtained with straight line trajectories. The rotational energy transfer originates primarily from collisions with small impact parameters. The observed rate constants for total collisional removal are in accordance with the collision complex model.

Experimental and Theoretical Study of State-Resolved Electronically Inelastic Collisions of Highly Rotationally Excited CN(A2Π) with Argon and Helium: The Role of Gateway Levels

A collaborative study of A → X electronic transitions from CN(A 2 Π,v=3,N=60-63) fine-structure A-doublet levels induced by collisions with argon and helium is presented. Experimental state-to-state rate constants were determined with an optical-optical double resonance technique. Specific levels of CN(A 2 Π,v=3,N=60-63) were prepared by excitation of the photolytically generated radical with a pulsed dye laser on various rotational lines in the A 2 Π-X 2 Σ + (3,0) band, and collisionally populated levels in the v A = 3 and the nearly isoenergetic v X = 7 vibronic manifolds were probed after a short delay by laser fluorescence excitation in the B-X (3,7) and B-A (3,3) bands. Final state distributions (relative state-to-state rate constants) are reported for CN(A)-Ar collisions; the rate constants for transitions induced by He were considerably smaller. Absolute total removal rate constants were also determined. A crossing of the A 2 Π v = 3 F 1 f rotational/fine-structure manifold with the X 2 Σ + v = 7 F 2 levels occurs at J = 62.5. The dependence of A → X rate constants and the total removal rate constants on the initial level demonstrates the importance of this gateway in facilitating collisions between these manifolds. The experimental CN(A)-Ar rate constants have been compared with theoretical rate constants computed in a quantum scattering treatment of the dynamics based on ab initio CN(A,X)-Ar potential energy surfaces. The small non-Born-Oppenheimer mixing of the A and X states in the isolated CN molecule was also included in the calculations. The computed total removal rates show an enhanced value for the perturbed N = 62 F,f initial level, in agreement with experiment, but the computed state-to-state rate constants do not agree well with the experimentally determined values.

State-resolved rotationally inelastic collisions of highly rotationally excited CN(A 2Π) with helium: Influence of the interaction potential

A collaborative experimental and theoretical study of rotationally inelastic collisions of CN (A 2Π, v=3, N=60–62) fine-structure Λ-doublet levels with helium is presented. Experimental state-to-state rate constants were determined with an optical–optical double resonance technique. The CN radical was prepared by 193 nm photolysis of BrCN diluted in slowly flowing helium at a total pressure of ∼0.3 Torr. Specific levels of CN(A 2Π,v=3,N=60–62) were prepared by excitation with a pulsed dye laser on various rotational lines in the A 2Π–X 2Σ+ (3,0) band, and collisionally populated levels were probed after a short delay by laser fluorescence excitation in the B 2Σ+–A 2Π (3,3) band. Final state distributions (relative state-to-state rate constants) are reported. To calibrate their magnitude, absolute total removal rate constants were determined. The measured rate constants were compared with theoretical rate constants computed in a quantum scattering treatment of the dynamics based on ab initio CN(A 2Π)–He potential energy surfaces. The agreement of measured and computed rate constants is very good. The state-to-state rate constants display propensities for conservation of the Λ-doublet and fine structure labels for the range of initial levels studied. The significant differences in the final state distributions in CN(A 2Π)–He collisions and the previously studied CN(A 2Π)–Ar system are shown to arise from differences in the interaction potentials for these two systems.

Experimental study of rotationally inelastic collisions of AlH(A 1Π) with Ar: State-to-state rate constants and Λ-doublet propensities

A study of rotationally inelastic collisions of AlH(A 1Π) with Ar is reported. AlH was prepared by 193 nm photolysis of trimethylaluminum diluted in slowly flowing Ar at ∼0.5 Torr total pressure. Specific rotational, Λ-doublet levels of AlH(A 1Π,v=0) were prepared by pulsed dye laser excitation on rotational lines in the AlH A 1Π–X 1Σ+ (0,0) band, and final levels were detected by spectrally resolving the fluorescence emission. Bimolecular state-to-state and total removal rate constants were determined. The state-to-state rate constants display dramatic Λ-doublet propensities. In particular, for high initial rotational levels the ΔJ=−1 f→e Λ-doublet symmetry changing transitions had significantly larger rate constants than for ΔJ=−1 f→f Λ-doublet symmetry conserving transitions. These Λ-doublet changing transitions are facilitated by curve crossing between the effective potential energy curves correlating with different rotational asymptotes. The total removal rate constants decrease with increasing initial J, reflecting the increasing rotational spacings.

Collisional Quenching and Energy Transfer of the z5DJo States of the Fe Atom

Room-temperature thermal rate constants for quenching and energy transfer have been determined for the individual fine-structure levels of the z5DJo term of the Fe atom in collisions with He, Ar, and several molecular gases (N2, O2, H2, and CH4). The z5DJo term is the upper level of a transition at 372 nm which is convenient for laser fluorescence detection of the Fe atom. Emission profiles from all excited levels were observed to be exponential, and total removal rate constants were derived. The rate constants for the molecular gases were significantly larger [in the range of (3−8) × 10-10 molecule-1 cm3 s-1] than for the inert gases [(0.3−1.3) × 10-10 molecule-1 cm3 s-1]. No evidence for collisional transfer to the neighboring b3H and a3D states was found, and upper limits for the collisional transfer rate constants are reported. Rate constants for intramultiplet transfer within the z5DJo state were determined for He and O2. The intramultiplet rate constants for He summed over all final fine-structure levels roughly equaled the total removal rate constants, while they were ∼10% of the total removal constants for O2.

Experimental and theoretical study of rotationally inelastic collisions of highly rotationally excited CN(A 2Π) with Ar

A collaborative experimental and theoretical study of rotationally inelastic collisions of CN(A 2Π,v=3,N=60) fine-structure Λ-doublet levels with argon is presented. Experimental state-to-state rate constants were determined with an optical–optical double resonance technique. The CN radical was prepared by 193 nm photolysis of BrCN diluted in slowly flowing argon at a total pressure of ∼0.9 Torr. Specific levels of CN(A 2Π,v=3,N=60) were prepared by excitation with a pulsed dye laser on various rotational lines in the A 2Π–X 2Σ+(3,0) band, and collisionally populated levels were probed after a short delay by laser fluorescence excitation in the B 2Σ+–A 2Π(3,3) band. Final state distributions (relative state-to-state rate constants) are reported. To calibrate their magnitude, absolute total removal rate constants and the large state-to-state rate constants for ΔN=−1 fine-structure conserving, Λ-doublet symmetry-conserving transitions were determined. The measured rate constants were compared with theoretical rate constants computed in a quantum scattering treatment of the dynamics with ab initio CN(A 2Π)–Ar potential energy surfaces. The agreement of measured and computed rate constants is very good. The rate constants display dramatic Λ-doublet propensities which depend upon the reflection symmetry of the initial level. From examination of coupled-state partial cross sections as a function of the projection quantum number specifying the angle of approach of the Ar atom to the CN plane of rotation, these propensities are shown to arise from a “helicopter” approach orientation which facilitates curve crossings between effective potential energy curves correlating with different rotational asymptotes.

First Determination of the Branching Ratios between Reactive Removal and Vibrational Relaxation in Collisions of OH(X2Πi, v = 1 and 2) with CH4

Absolute rate constants for reactive removal and vibrational relaxation have been determined for the collisions of OH({Chi}{sup 2}{Pi}{sub i}, {upsilon} = 1 and 2) with CH{sub 4}. The hydroxyl radical was produced in the reaction O({sup 1}D) + CH{sub 4} {r_arrow} OH({Chi}{sup 2}{Pi}{sub i}, {upsilon} {le} 4) + CH{sub 3} initiated by the 248 nm photolysis of O{sub 3} in the presence of CH{sub 4}. All the vibrational levels of OH({upsilon}) were detected by laser-induced fluorescence (LIF) via the sequences {Delta}{upsilon} = 0 ({upsilon}{double_prime} = 0, 1, and 2) and {Delta}{upsilon} = {minus}3 ({upsilon}{double_prime} = 3 and 4) of the {Alpha}{sup 2}{Sigma}{sup +}{minus}{Chi}{sup 2}{Pi}{sub i} transition. Temporal profiles of the LIF intensities were analyzed using a new linear regression method, and total removal rate constants for the vibrational levels ({upsilon} = 1--4) were determined. The linear analysis coupled with the previously reported nascent vibrational distributions of OH gave absolute rate constants for the reactive and nonreactive removal of OH({upsilon}). Rate constants for reactive removal, OH({upsilon}) + CH{sub 4} {r_arrow} products, were determined to be {kappa}({upsilon} = 1) = (2.1 {+-} 0.6) {times} 10{sup {minus}13} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} and {kappa}({upsilon}=2) = (0.9 {+-} 0.4) {times} 10{sup {minus}12} cm{supmore » 3} molecule{sup {minus}1} s{sup {minus}1}, and for vibrational relaxation, OH({upsilon}) + CH{sub 4} {r_arrow} OH({upsilon} {minus} 1) + CH{sub 4}, are {kappa}(1{r_arrow}0) = (3.5 {+-} 0.6) {times} 10{sup {minus}13} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} and {kappa}(2{r_arrow}1) = (1.1 {+-} 0.4) {times} 10{sup {minus}12} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. This article is the first report on the branching ratios between reactive removal and vibrational relaxation.« less

Collisions of O(1D) with HF, F2, XeF2, NF3, and CF4: Deactivation and reaction

The reactions of O(1D) atoms with fluorides have been investigated by time-resolved laser magnetic resonance (LMR). O(1D) atoms were produced by the dissociation of ozone with an excimer laser (KrF, 248 nm). By monitoring Cl atoms (when HCl or Cl2 is added) or FO radicals, the rate constants for total removal of O(1D) (×10−11 cm3/s) by HF(5.1±1.0), F2(0.81±0.20), XeF2(16±3.0), NF3(1.2±0.25), and CF4(<0.016) have been determined at 298 K. Reaction rate constants (×10−11 cm3/s) have been obtained for HF(1.5±0.3), F2(0.81±0.2), XeF2(14±3.0), and NF3(1.0±0.3). The deactivation of O(1D) by HX (X=F, Cl, Br) is discussed. Ab initio calculations have been performed with the aim of qualitative comparison of deactivation of O(1D) by F2 and Cl2.