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Vibrational relaxation of H

Vibrational relaxation of H2O(v2,v13) molecules by collisions with Ar was studied at 298 K (v2 denotes the bending vibrational mode and v13 denotes the sum of the symmetric, v1, and asymmetric, v3, vibrational modes). The H2O molecules from 14 different exothermic reactions of H-atom abstraction by OH radicals were observed by infrared emission from a fast flow reactor as a function of Ar pressure and reaction time. Numerical kinetic calculations were used to obtain rate constants for stretch-to-bend energy conversion, (v2,v13) → (v2 + 2,v13 − 1), and pure bend relaxation, (v2,v13) → (v2 − 1,v13). Rate constants for states up to v13 = 4 were based on the average values from all reactions. The rate constant for the (2,0) → (1,0) bending relaxation is in agreement with the published values from laser-induced fluorescent experiments; the rate constants for higher levels increase with v2. Our average rate constant for the (0,1) → (2,0) stretch-to-bend conversion is somewhat smaller but falls within the uncertainty limit of the published value. The average rate constants for the stretch-to-bend process for (01), (02), (03), and (04) stretching states are (4.3 ± 0.8) × 10−14, (7.7 ± 1.1) × 10−14, (14.3 ± 4.2) × 10−14, and (20.6 ± 6.2) × 10−14 cm3 molecule−1 s−1, respectively.

Stimulated emission (SE) induced by pulsed two-photon excitation of the 6p′[1/2]0, 6p′[3/2]2, 7p[1/2]0, 7p[3/2]2, and 7p[5/2]2 states of the Xe atom has been studied. Spectra of SE were recorded in the 800–3500 nm region, which covers the 6p′, 7p → 7s (2500–3500 nm), 6p′, 7p → 5d (1000–2000 nm), 7s → 6p (1200–1900 nm) transitions, as well as the near-IR 6p → 6s (800–1000 nm) transitions. It is shown that excitation of the 7p states results in radiative cascade via the 7s states, 7p → 7s → 6p, although at least one case of cascading via the 5d states is also observed. Spectra of SE induced by excitation of the 6p′ states are dominated by the 6p′ → 6s′ transitions in the near IR and the 6p′ → 5d[1/2]1 → 6p[1/2]1 → 6s[3/2]1 cascade; the 6p′ → 7s → 6p cascade is also observed, although the secondary 7s → 6p emission is rather weak in comparison with excitation of the 7p states.

The total quenching rate constants of argon atoms in the 4p′[1/2]0, 4p[1/2]0, 4p[3/2]2, and 4p[5/2]2 states (2p1, 2p5, 2p6, and 2p8, respectively, in the Paschen numbering system) by rare gases, H2, D2, N2, CO, NO, O2, F2, Cl2, CO2, NO2, CH4, C2H2, C2H4, C2H6, CF4, CHF3, and SF6 have been determined at room temperature. These four excited states of argon (energy 13.09–13.48 eV) were selectively prepared by two-photon excitation from the ground state using VUV (184–190 nm range) laser pulses. The total quenching rates were deduced from the pressure dependence of the decay times of the excited-state atoms, measured by observing their fluorescence emission intensities in the presence of added reagents. The quenching constants increase from values of ≅0.01×10−10 cm3 atom−1 s−1 for Ne, to ≅0.1×10−10 cm3 atom−1 s−1 for He and Ar, and to very large values, (5–15)×10−10 cm3 atom−1 s−1, for most polyatomic molecules, F2, Cl2, and O2. The quenching mechanisms of the Ar(4p,4p′) atoms are briefly discussed and compar...

The optical–optical double resonance method has been used to excite selected vibrational levels of the E(0+) and f(0+) ion-pair states of ClF. Subsequent bound–free transitions terminating on three repulsive valence states, Y(3Σ0+−), B1(3Π0+), and C(1Σ0++), have been analyzed. The bound–free continua have been modeled to obtain analytical expressions for the three 0+ repulsive potentials and to improve the description for the E(0+) and f(0+) state potentials. One of the repulsive states is Y(3Σ0+−), which is responsible for the predissociation of B(3Π0+). The transition dipole functions also have been assigned for the bound–free transitions. The molecular orbital configurations of the lower states are discussed. Finally, the influence of homogeneous interaction between the E(0+) and f(0+) states on the bound–free spectra from certain vibrational levels is discussed.

The room-temperature reactions of OH(OD) radicals with cyclo-C6H12, n-C4H10, and neo-C5H12 have been investigated by observing the infrared chemiluminescence from the H2O(HOD) molecules generated in a fast-flow reactor. These hydrocarbon molecules are representative for abstraction from secondary and primary C–H bonds. The total vibrational energy released to H2O(HOD) was in the range of 〈fv〉=0.55–0.65. The majority (80%–85%) of the vibrational energy is in the stretching modes and the main energy release is to the local mode associated with the new OH bond. The dynamics associated with the energy disposal to H2O(HOD) resemble the H+L−H dynamics for the analogous reactions of F atoms. The data from H2O and HOD are complementary because of the different collisional coupling between the energy levels of the ν1, ν2, and ν3 modes; however, no specific isotope effect was found for the energy disposal to H2O versus HOD for reactions with the hydrocarbon molecules. In contrast, a very unusual isotope effect was ...

Four of the six ion-pair states of ClF that correlate to Cl+(3PJ) and F−(1S0), the E(0+,3P2), f(0+,3P0), β(1,3P2), and G(1,3P1) states, have been identified by sequential, two-photon excitation via the ClF(B 3Π0+) valence state. The Ω=1 states, β and G, were studied by selection of rotational levels of the B 3Π0+ state that are perturbed by ClF(A 3Π1). Spectroscopic data from laser excitation and fluorescence spectra permit the assignment of vibrational energies and rotational constants to 30 levels. These four ion-pair states exhibit extensive homogeneous and heterogeneous interactions, and neither the vibrational energy nor the rotational constants are regular with increasing vibrational quantum number. The vibrational and rotational constants of the A 3Π1 state were identified from the low resolution ClF[β(1)−A 3Π1] emission spectra, and the dissociation limits of the A 3Π1 and B 3Π0+ states are compared. The dissociation energy of ClF(X) is confirmed to be 21 110 cm−1. Some qualitative information als...

The infrared chemiluminescence of vibrationally excited H2O and HDO from the highly exothermic reactions of OH and OD radicals with HI and GeH4 was observed in the 2200–5500 cm−1 range. The experiments utilized a fast-flow reactor with 0.3–1 Torr of Ar carrier gas at 300 K; the OH(OD) radicals were produced via the H(D)+NO2 reaction and the H or D atoms were generated by a discharge in a H2(D2)/Ar mixture. The H2O and HOD vibrational distributions were determined by computer simulation of the emission spectra in the 2200–3900 cm−1 range. The total vibrational energy released to H2O and HOD molecules is, respectively, 〈fv〉=0.36 and 0.41 from HI and 〈fv〉=0.46 and 0.51 from GeH4. These values are significantly smaller than for the reactions of OH and OD with HBr, 〈fv〉=0.61 and 0.65. The populations of the O–H stretching vibration of HOD and the collisionally coupled ν1 and ν3 stretching modes of H2O decrease with increasing vibrational energy. In contrast, the vibrational distribution from the HBr reaction i...

The quasiclassical trajectory (QCT) method was used to study the dynamics of the OH(X 2Π) and OD(X 2Π)+HBr chemical reactions on an empirical potential energy surface (PES). The main emphasis in the calculation was the vibrational energy distributions of H2O (and HDO) and the magnitude and temperature dependence of the rate constant. However, this PES also serves as a generic model for the dynamics of direct H atom abstraction by OH radicals. Since this PES has no formal potential energy barrier, variational transition‐state theory was used to obtain rate constants for comparison with the QCT calculations and experimental results. The parameters of the potential energy surface were adjusted to obtain better agreement with the experimentally measured fraction of H2O vibrational energy, 〈fV(H2O)〉=0.6, without significantly changing the entrance channel. No isotope effect for the partition of energy to H2O vs HOD was found. Analysis of the trajectories indicates that the reactant OH(OD) bond is a spectator, ...

Vibrationally excited H2O, HOD, and D2O molecules formed by unimolecular elimination from deutero‐substituted ethanol molecules C2H5OH*, C2H5OD*, CH2DCH2OH*, and CH2DCH2OD* with an excitation energy of about 100 kcal mol−1 were observed by infrared chemiluminescence in the 2400–3900 cm−1 range. The activated ethanol molecules were produced via the successive reactions H+CH2ICH2OH→HI+CH2CH2OH and H+CH2CH2OH→CH3CH2OH* in a fast flow reactor that was observed with a Fourier transform spectrometer. The vibrational distributions of the H2O, HOD, and D2O molecules were determined by computer simulation of the experimental spectra; the distributions decline with increasing vibrational energy giving 〈fv〉=0.15 and 〈fv〉=0.14 for H2O and HOD from the decomposition of C2H5OH* and C2H5OD*, respectively. The vibrational energy in the bending mode of H2O is comparable to the energy in the stretching modes. Comparison with the statistical vibrational distributions shows a substantial overpopulation of the bending levels ...

A new, simple method for the generation of Xe(6s[3/2]1) and Xe(6s′[1/2]1) atoms is described. The method involves resonant two‐photon excitation of Xe(6p[1/2]0 and 6p′[3/2]2) states followed by amplified spontaneous emission (ASE) to the Xe(6s[3/2]1 and 6s′[1/2]1) states. The vacuum ultraviolet transitions, Xe(6s[3/2]1→5p6(1S0)) at 147 nm and Xe(6s′[1/2]1→5p6(1S0)) at 129.6 nm, were used to monitor the time dependence of the resonance state atom concentrations. The quenching rate constants of these resonance atoms with ten molecules were measured at 300 K. The quenching cross‐sections of the Xe(6s and 6s′) resonance atoms are compared to the cross‐sections of the metastable Xe(6s[3/2]2) atoms and Xe(6p[3/2]2) atoms. The correlation between quenching cross‐sections and photoabsorption cross‐section of the molecules predicted by the resonance dipole–dipole energy transfer model is discussed. The applicability of the two‐photon driven ASE method for the generation of other resonance state atoms is considered.

One‐photon laser excitation of Xe(6s[3/2]2) and Kr(5s[3/2]2) atoms that were generated in a discharge‐flow reactor was used to study the collisional relaxation of the Kr(5p′[3/2]1, [3/2]2, and [1/2]1), the Xe(7p[3/2]2, [3/2]1, [5/2]2, and [5/2]3), and the Xe(6p′[3/2]1, [3/2]2, and [1/2]1) states in He and Ar. Both cw and pulsed laser excitation techniques were utilized to obtain the total deactivation rate constants and product formation rate constants at 300 K. Collisions with He mainly produce Xe* and Kr* product states with small energy defects, but the rate constants can be as large as 20×10−10 cm3 atom−1 s−1, which correspond to thermally averaged cross sections of 150 A2. Because of the rapid collisional coupling of populations in nearly isoenergetic levels, multicomponent exponential decay of the initially produced state is frequently observed. The deactivation rate constants for Ar are smaller than for He, but the product distributions tend to be more diverse than for He, and arguments based only ...

Emission spectra have been used to characterize the excitation‐transfer reactions from Kr(5s’,3P0) and Kr(5s,3P2) metastable atoms to 12CO and 13CO at 300 K. The most important products from the Kr(3P0) reactions are 12CO and 13CO(b 3Σ+,v’=0 and 1) and 12CO(a’ 3Σ+,v’=34 and 35) and 13CO(a’ 3Σ+,v’=35 and 36). The rotational distributions of the CO(a’ 3Σ+) and CO(b 3Σ+,v’=1) levels are cold, but the CO(b 3Σ+,v’=0) distribution is rotationally excited. The populations in the 12CO(a’,v’=34 and 35) levels are transferred to CO(b,v’=0) by collisions with He and the rate constants are 0.4–1.0×10−10 cm3 s−1. Emission spectra from the Kr(3P2) reaction identified 12CO(a’,v’=23–26) and 13CO(a’,v’=24–27) and CO(d 3Δ,v’=20 and 21) for both 12CO and 13CO as important products; the CO(d 3Δ,v’=20 and 21) states previously were identified by Tsuji and co‐workers. The vacuum ultraviolet spectra from the Kr(3P2) reaction with 12CO and 13CO showed that CO(A 1Π) is a primary product and that it also is formed from CO(d 3Δ) an...

The two‐photon, laser‐assisted reaction between Xe and Cl2 has been used to generate XeCl(B,C) molecules for subsequent kinetic studies at 300 K. Two‐body quenching rate constants for the collisionally coupled XeCl(B,C) molecules were determined from the pressure dependence of their decay rates on added molecular gases. The quenching constants for XeCl(B,C) by most molecules are large, even though acceptor electronic states are not available for quenching by an excitation‐transfer mechanism. At higher pressure (>100 Torr) of Xe, Xe2Cl(4 2Γ) molecules were formed via three‐body quenching of XeCl(B,C), and the quenching rate constants for Xe2Cl(4 2Γ) by added gases were determined and compared with those for XeCl(B,C). In all cases, the quenching rate constants for XeCl(B,C) are larger. The two‐body quenching mechanisms for XeCl(B,C) and Xe2Cl(4 2Γ), which are ionic molecules, are discussed. Three‐body quenching of XeCl(B,C) with formation of Xe2Cl(4 2Γ) was observed for Xe+N2, Xe+CF4, and Xe+SF6.

The generation and decay of Kr(3P2) and Kr(3P0) atoms in a flowing afterglow reactor at 300 K using He carrier gas have been characterized and compared with Ar carrier gas. The dominant loss for the Kr(3P2) and Kr(3P0) atoms in He is diffusion to and quenching at the wall; the two‐body quenching constants are of the order of 1×10−15 cm3 s−1 for each. The Kr(3P0) concentration in He carrier was sufficiently high that the total quenching rate constants were measured without resorting to optical pumping from the lower energy Kr(3P2) state. Room temperature rate constants are reported and the product states are discussed for the Kr(3P2) and Kr(3P0) reactions with Xe, CO, N2, H2, CF4, and CH4; the difference between the Kr(3P0) and Kr(3P2) rate constants for N2 is nearly a factor of 6. Quenching rate constants for 13CO are ∼25% smaller than those for 12CO. The Kr(3P0) reaction with CO gives mainly CO(b 3Σ+) and (e 3Σ−); the CO(b, v’=0) level is much more rotationally excited than CO(b, v’=1). Excitation‐transf...

The decay kinetics of the Xe(6p[1/2]0 or 2p5), Xe(6p[3/2]2 or 2p6) and Xe(6p[5/2]2 or 2p9) states have been studied in He and Ne buffer gas using the two‐photon laser‐excitation technique. The pressure dependence of the fluorescence decay rates was used to measure the total quenching rate constants at 300 K. The primary product distribution from two‐body collisions with He or Ne were estimated from product fluorescence intensities, and state‐to‐state quenching rate constants were assigned. Limited information about the decay kinetics of the Xe(2p7),Xe(2p8), Xe(2p10) states was inferred from observation of the decay of these product states at various He and Ne pressures. With the exception of Xe(2p5) in He and Ne and Xe(2p7) in He, the decay constants of the Xe(6p) states are less than 1.0×10−11 cm3 s−1, and these rate constants are smaller then the decay constants for heavier rare gases. The collisional depolarization of Xe(2p6) by Ne was studied by monitoring the decay rates of the vertical and horizonta...

The two‐photon, laser‐assisted reaction between Xe and Cl2 has been used to prepare XeCl (B,C) molecules in Xe and in Xe mixtures with lighter rare gases for kinetic studies of the coupled XeCl (B,C) states. The XeCl (B–X) spectra were used to assign the conditions for which the vibrational temperature was nearly 300 K. Relative intensity and coupled radiative lifetime measurements provide independent data which support an energy separation between the XeCl(B) and XeCl(C) states of ∼100 cm−1. The two‐body quenching rate constant in Xe for XeCl (B,C) was measured as 5+3−2×10−12 cm3 s−1, and a three‐body quenching rate constant of 13±4×10−31 cm6 s−1 is indicated. Experiments also were done with added Kr, Ar, Ne, and He to establish two‐body and mixed (e.g., Xe+Ar) three‐body quenching rate constants. The three‐body quenching rate constants are nearly equal to the Xe2Cl* formation rate constants and three‐body dark quenching of XeCl(B,C) is negligible.

The quenching kinetics of the Xe(6p[1/2]0 ), Xe(6p[3/2]2 ), and Xe(6p[5/2]2 ) states have been studied in Kr and Ar buffer gas at room temperature using the two‐photon, laser‐excitation technique. The total quenching rate constants and the primary product distributions were measured to obtain state‐to‐state rate constants. Collisions between Xe[1/2]0 and Kr mainly gave energy transfer to Kr(5s,3P2 ) rather than relaxation to the Xe(6p or 5d) levels. The transfer of energy from Kr(5s,3P2 ) back to the Xe(6p) manifold also was observed. The collisional coupling between Xe[1/2]0 and Xe(3d5 ) in Ar, reported previously, was confirmed. The collisions of Kr and Ar with Xe[3/2]2 and Xe[5/2]2 atoms gave intramultiplet relaxation; observation of the time dependence of the primary products, the Xe[3/2]1, [5/2]3, and [1/2]1 states, permitted assignment of some state‐to‐state rate constants for these states. The flow of energy through the Xe(6p) manifold is discussed.

HF infrared chemiluminescence from the reactions of F atoms with HCl, HBr, and HI was used to assign vibrational–rotational populations of the HF product. Experiments were done in both a cold‐wall, arrested vibrational–rotational relaxation apparatus and in a fast‐flow, arrested vibrational relaxation apparatus. Since the total HF formation rate constants are known for these reactions, absolute 300 K rate constants for formation of HFvJ are established. The mean vibrational energy disposal to HF including estimates for HF (v=0) is

Room temperature rate constants (thermal average cross sections) for the quenching of electronically excited state rare gas metastable atoms by mercury atoms have been measured using the flowing afterglow technique. The thermal cross sections are σQ[Ne(3P2)]=70 A2;σQ[Ar(3P2)]=194 A; σQ[Ar(3P0)]=219 A2; and σQ[Kr(3P2)] =124 A2. The mechanism for quenching by mercury atoms is Penning ionization for Ne* and Ar*, and excitation transfer for Kr*. These results are discussed in terms of the cross section of similar reagents and the cross section predictions of the close collision criteria. The large experimental cross sections indicate that the total quenching cross section is dictated by interactions occuring at large internuclear distances associated with a long range attractive potential. However, the interactions at shorter range are responsible for the actual conversion from reactants to products. The Kr(3P2) +Hg excitation transfer reaction provides a way to generate Hg(3P2) metastable atoms in a flowing afterglow apparatus.

The H+ClO and SF reactions have been isolated and studied by infrared chemiluminescence in a fast flow reactor. The OH product channel is favored over the HCl channel by a factor of 4.5 and the total rate constant is (7.7±1.9)×10−11 cm3 s−1 for the H+ClO reaction. Both sets of products are accessed from a bound singlet intermediate with HCl+O(3 P) formed by a singlet–triplet surface crossing in the exit channel; the energy disposal is 〈fV (OH)〉=0.45 and 〈fV (HCl)〉=0.31. The H+SF reaction gives only HF+S(3P), but the energy disposal differs dramatically from the HCl channel of the ClO reaction. This difference arises from changes in the thermochemistry, which result in an earlier crossing to the HSF triplet surface followed by release of repulsive energy as the HF separates from the S(3P) atom.

The radiative lifetimes and collisional deactivation rate constants, in argon, of eight Kr(4p5[2P1/2]5p and [2P3/2]5p) levels have been measured by a time‐resolved laser‐induced fluorescence technique in a flowing afterglow apparatus. The measured radiative lifetimes are compared with other experimental values and with theoretical calculations. Radiative branching ratios of these excited states also were measured in order to assign the absolute transition probabilities of the Kr(5p,5p′–5s, 5s′) transition array from the radiative lifetimes. In addition to the total deactivation rate constants, product states from two‐body collisions between Kr(5p and 5p′) atoms and ground state argon atoms were identified from the laser‐induced emission spectra, and product formation rate constants were assigned. Two‐body intermultiplet transfer from Kr(4p5[2P1/2]5p) to the Kr(4p5[2P3/2]4d) levels occurs with ease. Intermultiplet transfer from the lowest level in the (4p55p) configuration to the Kr(4p55s and 5s′) manifold...

The low pressure KrF emission spectra, which includes the KrF(III,1/2−I,1/2 or B–X) and the KrF(II,3/2−I,3/2 or C–A) transitions arising from the reaction of metastable or resonance states of Kr with F2, NF3, and CF3OF, have been simulated by computer. Since a broad distribution of very high v′ levels is produced by the chemical reactions, the dependence of the spectrum upon various properties of the upper and lower states was first investigated. A general discussion of the types of emission spectra that can be expected from bound‐free transitions from high v levels is first presented. As a starting point for fitting the KrF spectra, the a b i n i t i o potential curves and the dependence of the transition moments upon internuclear separation calculated by Hay and Dunning for KrF were used. The I,1/2 and III,1/2 curves are generally satisfactory but some modification of the I,3/2 potential curve was necessary in order to fit the observed spectra. As the final step, KrF* vibrational distributions from the Kr*+F2, CF3OF, and NF3reactions were assigned that gave simulated spectra in agreement with the low pressure spectra. The fraction of the available energy released as KrF* vibrational energy was ≳50%. The assignment of the initial vibrational distribution as well as 〈f V 〉, and to the dependence of the transition moment upon internuclear separation. Within some general limitation, this spectrum is not very sensitive to the I,1/2 or III,1/2 potential curves.

Laser excitation from N2(A 3Σ+u, v=0–6) in Ne and Ar carrier gas in a flowing afterglow apparatus has been used to prepare N2(B 3Πg) molecules in individual levels from v=3–10. The subsequent N2(B–A) fluorescence intensity was observed to study the coupling and relaxation kinetics of N2(B 3Πg, v=2–10). The decay curves from each level show double (or higher) exponential relaxation. The first component is assigned as primarily the rapid coupling of the N2(B 3Πg,v) and N2(W 3Δu, v or v+1) levels, however, the N2 (B′ 3Σ−u, v−4) levels also may be involved for N2(B, v≥5). The slowest decay component represents the subsequent relaxation of the coupled levels. The combination of the two steps is equivalent to apparent stepwise vibrational relaxation of N2 (B 3Πg, v), such relaxation occurs even at low Ar pressures because of the large rate constants and long radiative lifetimes of N2(B) and N2(W). The coupling pattern between N2(B) and N2(W) is analyzed, and rate constants are assigned to elementary steps in th...

The radiative lifetimes and collisional deactivation rate constants by argon of four Xe(5p 5[2P3/2]6p), three Xe(5p 5[2P1/2]6p), and three Xe(5p 5[2P3/2]7p) levels, hereafter referred to as Xe(6p), Xe(6p′), and Xe(7p) states, have been measured by a time‐resolved laser‐induced fluorescence technique in a flowing afterglow apparatus. The deactivation rate constants of the 6p levels are in the (0.5–5)×10−11 cm3 s−1 range; however, the rate constants for the 6p′ and 7p levels are much higher with values of (15–40×10−11 cm3 s−1. Product states resulting from two‐body collisions between the laser excited Xe(6p, 6p′, and 7p) atoms and ground state argon atoms were identified from the product emission spectra. In addition to intramultiplet relaxation, considerable intermultiplet transfer to the 6s′ levels seems to occur for the Xe(6p) states. Both intramultiplet relaxation and intermultiplet transfer (to the 6d, 5d, and 7s manifolds) are important for the Xe(6p′) and Xe(7p) states. Radiative branching ratios for...

The XeCl (B–X) and (C–A) emission spectra obtained from reaction of Xe (3P2 or 3P1) with Cl2, CCl4, and COCl2 in the presence of He, Ne, Ar, Kr, and N2 bath gases were used to study the vibrational relaxation and transfer between the B and C states of XeCl. By using the different Cl donors, different ranges of vibrational energy were emphasized. The bound–free emission spectra were simulated for various pressures of bath gas to obtain vibrational distributions. Numerical modeling of the XeCl(B) and XeCl(C) vibrational populations and the B/C intensity ratio as a function of pressure gave rate constants for vibrational relaxation and transfer, as well as the model for the state‐to‐state processes. For Ar as the bath gas, vibrational relaxation can be characterized by an exponential gap model Pij ∝ e−0.1ΔE/kT, with rate constants of (1–6), (6–12), and (20–30) × 10−11 cm3 molecule−1 sec−1 for the v ranges of 0–30, 30–70, and 70–130, respectively. The rate constants for electronic state transfer are (3–11), (...

The infrared emission intensities from the reaction F+GeH4 have been used to measure the energy partitioned to the HF product. The experiments were conducted in a cold‐walled reactor with various flow rates of GeH4 and fluorine atom source (discharged SF6 or CF4). Based on the highest observed HF vibrational‐rotational level, D(H–GeH3) was estimated as ≤78 kcal mole−1. The initial relative vibrational populations were N(ν = 1): N(ν = 2): N(ν = 3): N(ν = 4): N(ν = 5) = 0.10:0.18:0.29:0.41: 0.02. Based upon D(H–GeH3) = 78 kcal mole−1, the mean fractional conversion of energy into HF vibrational energy was 0.58. The rotational distributions extend to quite high J levels; after correction for some rotational relaxation the mean fractional conversion to HF rotational energy was estimated as 0.12.

Sensitized reactions of Xe and Kr with halogen donors in the presence of high buffer gas pressures of Kr and Ar, respectively, have led to the observation of five emission bands in the ultraviolet region of the spectrum. These broad structureless bands are assigned to the mixed rare gas–halide trimers KrXeCl, KrXeBr, KrXeI, ArKrF, and ArKrCl. Despite an extensive search, no emission corresponding to KrXeF could be found and this mixed trimer may be unstable because of interaction with a lower repulsive state. The positions and half‐widths of the five emission bands are characterized, and the formation mechanism of the mixed trimers in these experiments is discussed.

The product channels from interaction of metastable argon atoms (3P2,0) with a series of chlorine containing molecules (Cl2, NOCl, ClO, HCl, CCl4, PCl3, and SnCl4), as well as some other molecules (Br2, N2O, NO2, H2S, and COS), have been investigated by emission spectroscopy. The rate constants for product channels were established by comparison of the emission intensities from the excited state products to the emission intensities from excited state Kr atoms, which have known rate constants for excitation by metastable argon atoms. Comparison of the individual product rate constants with previously determined total quenching rate constants of Ar(3P2,0) gave the branching ratios for emitting product channels. Although our measurements include the wavelength range from 120–800 nm, emphasis is placed upon the vacuum ultraviolet region and upon the ArCl*, ArBr*, and ArO* product channels. The highest ArCl* yield, ∼50%, was obtained for Cl2 and ClO. Quenching mechanisms for the halogen containing reagents are...

Laser induced fluorescence studies have been done with XeCl molecules, which demonstrate photoassociation (free–bound absorption) as well as conventional bound–bound absorption from the XeCl(X) van der Waals molecules. The XeCl(X) and Xe+Cl pairs were generated by a pulsed dc discharge through 1–6 Torr Xe/Cl2 mixtures. Experiments also were done with Xe/HCl mixtures. The time and wavelength resolved XeCl(B–X) and XeCl(C–A) excitation and fluorescence spectra are reported. Model calculations were done to demonstrate that the laser excitation spectra for XeCl(B,v=0−3) show laser‐assisted photoassociation. The time resolved decay of the XeCl(B,v′=0) and XeCl(C,v′=0,1) states was used to measure the radiative lifetimes 11.1±0.2 and 131±10 ns, respectively, and the XeCl(B) and XeCl(C) coupling and quenching rate constants. The transfer and quenching rate constants for XeCl(B) by Xe are assigned as (11±1)×10−11 and (2.3±0.3)×10−11 cm3 molecule−1 s−1, respectively; although, the sum is known with greater certain...

The N+2(B 2Σ+u–X 2Σ+g), CO+(B 2Σ+–X 2Σ+), and CO+(A 2Π–X 2Σ) emission spectra excited by reaction of He+ and He++He+2 mixtures with N2 and CO are compared with the spectra from the reaction with He(2 3S) metastable atoms. The experiments were done in a room temperature flowing afterglow apparatus. Charge exchange between He+ and N2 gave N+2(B) and a small amount of N+2(D) in addition to N+2(C); the yield of N+2(A) was insignificant. The vibrational population distribution of N+2(B) excited by He+ differed greatly from that given by the reaction with He(2 3S). No CO+ emission could be identified from the He++CO reaction. The reaction of He+2 with N2 and CO gave strong emissions from N+2(B), CO+(B), and CO+(A) with vibrational populations resembling the distributions expected for Franck–Condon transitions from neutral N2 and CO. Although the N+2(A–X) emission could not be studied in detail, N+2(A) appeared to be a product from reaction of He+2 and N2.

The bound–free XeCl spectra observed from the reactions of Xe(6s, 3P2) atoms with Cl2, PCl3, CCl4, and COCl2 have been compared to computer simulated spectra in order to assign the XeCl* vibrational energy distributions from these reactions. The 〈fV〉 values for the initial state distributions are between 0.6–0.8 for Cl2 and CCl4 and 0.2–0.3 for COCl2. The results for PCl3 are unusual in that the distribution for the XeCl (B) and XeCl (C) states apparently differ, with the 〈fV values being ∼0.47 and 0.64, respectively. This selection of reactions represents most types of XeCl spectra that have been observed and the vibrational energy disposal to XeCl by other Xe( 3P2) + RCl reactions can be estimated by comparison with these results. Model potentials, as well as the ab initio potentials of Hay, were used to represent the XeCl states for the simulation. Simulations were done for both the XeCl (B,1/2–X,1/2) and for the XeCl (C,3/2–A,3.2) transitions. The XeCl (B,1/2–X,1/2) transition is the more useful fo...

One‐photon excitation in the afterglow of a pulsed discharge and two‐photon excitation in a static cell have been used to generate the six Xe(5p56p) states in variable pressures of Xe. The decay times of the initially excited states and their products have been analyzed to obtain state‐to‐state rate constants at 300 K for collisional transfer among the Xe(5p56p) levels and the Xe(5p56s’) levels. The depolarization rate constants for the Xe(5p[5/2]2) and Xe(5p[3/2]2) states prepared by two‐photon excitation were measured to be ∼6×10−10 cm3 molecule−1 s−1. The collisional deactivation rate constants of the two‐photon prepared states, Xe(6p[1/2]0), Xe(6p[3/2]2), and Xe(6p[5/2]2), in Ar also are reported.

The decay rates of Ar(3P2), Ar(3P0), Kr(3P2), and Xe(3P2) metastable states in argon carrier gas have been measured in a flowing afterglow apparatus. From analysis of the dependence of the pseudo‐first‐order decay constants upon pressure, the diffusion, two‐body, and three‐body rate constants have been assigned for each metastable state in Ar. The rate constants found for Ar(3P2) agree with the values accepted in the literature for these processes. The two‐body rate constants for Kr(3P2) and Xe(3P2) are a factor of 4 lower than for Ar(3P2). The three‐body rate constants for Kr(3P2) and Xe(3P2) are reduced by factors of 10 and 100, respectively, relative to the Ar(3P2) rate constant. The reduction in three‐body constants for Kr(3P2)+2Ar and Xe(3P2)+2Ar is consistent with the reduced binding energy of KrAr* and XeAr*. The diffusion and three‐body coefficients for Ar(3P0) are equal to those for Ar(3P2), but the two‐body rate constant is 2.5 times larger than for Ar(3P2). The results for each of the three pro...

The radiative lifetimes and collisional deactivation rate constants of Ar[3p5(2P01/2)5p] and Ar[3p5(2P03/2)5p] levels with argon atoms have been measured by time resolved laser induced fluorescence combined with a pulsed discharge for preparation of populations in the Ar(4s) precursor levels. The radiative lifetimes of Ar(5p) levels are 100–140 ns, and their two‐body deactivation rate constants are in the range of (1.2–5.6)×10−10 cm3 atom−1 s−1. About half of the two‐body energy transfer is intramultiplet relaxation. Only about 20% of the Ar(5p) radiative decay is via 5p–4s transitions; the reminder is via transitions to the 5s and 3d states. The radiative cascading through the 5s and 3d states populates the 4p states with conservation of the inner core configuration. From the time dependence of the emission intensities from the 4p levels, the radiative lifetimes of the 5s and 3d states were estimated to be ∼50 ns.

The XeBr and XeI emissions spectra have been recorded in a flowing afterglow apparatus from the reaction of Xe(3P2) atoms with 16 bromine and iodine containing reagents. In all cases both the B and C states of XeI and XeBr are observed; the inital B/C ratio is ∼1.5. The ratio increase with pressure because of collisional transfer from C to B. Comparison of the total XeBr and XeI emission intensities with the XeC1 emission intensity from Xe(3P2)+C12 is used to obtain rate constants for XeBr and XeI formation. The branching fractions for XeI and XeBr formation are large, probably unity, for Br2, I2, IC1, and IBr and relatively small for the polyatomic molecules except for CF3I and possible CBr4. From the short wavelength limit of the B–X spectra, upper limits to D0(R–Br) and D0(R–I) are assigned. The theoretical potential curves calculated by Dunning and Hay for the A, B, C, and X states of XeI and XeBr were slightly adjusted so that good agreement was obtained between the simulated and experimental spectra...

The radiative lifetimes and two‐body deactivation rate constants of the Ar(3p54p and 4p′) levels have been measured by a time‐resolved laser‐induced fluorescence technique in a flowing afterglow apparatus. The flowing afterglow produced the Ar(3p54s,3P2) metastable atoms, which subsequently were pumped by the pulsed dye laser. The measured radiative lifetimes are in excellent agreement with the calculated transition probabilities based upon intermediate‐coupling theory. Radiative branching ratios of these states also were measured in order to assign the transition probabilities and the absorption oscillator strengths of the transitions between the 4s and 4p levels. The two‐body deactivation rate constants range from 1×10−10 to 2×10−11 cm3 atom−1 sec−1. Specific product states from the two‐body collisions between Ar(4p and 4p′) atoms and Ar were identified from the laser‐induced emission spectra and rate constants for individual product states were assigned for each level. Our results show that two‐body co...

The HgX(B 2Σ+–X 2Σ+), X=halogen, emission spectra have been recorded from Hg(3P2) atom reactions with several halogen containing molecules using a flowing afterglow reactor. The HgX* emission intensities were compared with the HgCl* emission intensity from Hg(3P2)+Cl2 to assign rate constants for HgX(B) formation. The Hg(3P2)+ diatomic halogen reactions have large kHgX* and their branching fractions for HgX(B) formation are probably unity. The polyatomic reagents generally gave much smaller kHgX*; although, a few moderately good donors, e.g., CF3I, CBr4, CCl4, and NF3 were identified. The experimental spectra were numerically simulated to assign HgX(B) vibrational energy distributions. A decrease in 〈fV(HgX)〉 was found for the Cl2, Br2, I2 series which is analogous to previous findings for 〈fV(XeX)〉 from reactive quenching of Xe(3P2). Possible reasons for the similarity are discussed. The HgX(B) vibrational energy disposal for polyatomic reagents is compared to analogous data for reactions of alkaline ear...

HF infrared chemiluminescence has been utilized to study the energy disposal for the abstraction of hydrogen by fluorine atoms from polyatomic molecules which yield radical fragments with large stabilization energies. The prototype systems selected for study, methyl benzenes, phenol, and acetonitrile, are cases which yield resonance stabilized radicals as products. Comparison is made to the energy disposal from the reaction of F with the primary C–H bonds of aliphatic hydrocarbons, which have smaller radical stabilization energies. In general the radical stabilization energy, which is associated with major changes in geometry of the radical relative to the parent molecules, was not available to the HF product. The reactions of F + benzene and ethylene also were studied to provide reference data for different types of C–H bonds. The HF vibrational energy distributions have been interpreted using an extension of the information theory which previously has been applied to three body reactions. Vibrational surprisal analyses are developed and discussed for three models of the reference (prior) product distributions: (i) the polyatomic fragment product was treated as an atom, i.e., the three body case, (ii) the rotations of the radical fragment were added to the three body model, (iii) a complete model including all vibrational and rotational modes of the polyatomic radical fragment. For (iii) with the use of the full thermochemical exoergicity linear surprisal plots were found and these plots were used to assign relative populations to HF (v=0). The information‐theoretic parameters from the three reference models are compared for a series of F+HR reactions in which R increases in complexity from Cl to CH2C6H5. For reactions with large product stabilization energies, calculations for (i) and (ii) were done with a reduced ’’effective available’’ energy corresponding to the assumption that the energy available to HF was less than the full exoergicity. Some insight is gained into the role of the R fragment in the energy disposal.

Optical pumping has been used to select Ar atoms in the metastable 3P2 or 3P0 state in a flowing afterglow reactor. The relative concentrations of the two metastable states were assigned from observation of the N2(C,v’) emission spectra. The isolated reactions of the Ar(3P2) and Ar(3P0) atoms with F2, NF3, Cl2, CCl4, PCl3, and SOCl2 were examined at 300 K by observation of ArCl* and ArF* formation. The total quenching rate constants for Ar(3P0) are slightly larger than for Ar(3P2). The Ar(3P2) atom reactions give only the B and C states of ArF* and ArCl*; the Ar(3P0) atom reactions give a mixture of B, C, and D states with B and D being favored. Thus, a propensity for conservation of the Ar+ ion–core configuration was found. The branching fraction for ArX* formation from Ar(3P0) with Cl2, SOCl2, F2, NF3 are similar, but those for PCl3 and CCl4 are smaller, relative to Ar(3P2). Improved rate constants for formation of individual N2(C,v’) levels from Ar(3P0) and (3P2) reacting with N2 at 300 K are given in ...

Infrared chemiluminescence from the HF, HCl, and OH products has been used to measure the nascent vibrational distributions and the rate constants at 300 K for the title reactions in a fast flow reactor. The ClO reaction was observed as a secondary step in the ClO2 and Cl2O systems. The reactions proceeding by a direct mechanism, Cl2O, ClNO, OF2, and CF3OF release relatively small fractions, ∼0.37, of the available energy as HCl or HF vibrational energy with narrow distributions, in accord with the dynamics associated with the H atoms on a repulsive potential surface. The ClO2 and NO2 reactions, which proceed by short lived intermediates, release a larger fraction of vibrational energy to OH and with broad distributions. Although the data for the ClO reaction are not definitive, the OH formation channel is the more important by a factor of 4–5. The NO2 reaction was studied in direct comparison with Cl2 to choose the best Einstein coefficients of OH by comparing the OH and HCl formation rate constants.

The HgX(B 2Σ+–X 2Σ+), X=Cl, Br, I, spectra from the dissociative excitation reactions of N2(A 3Σ+u, v=0, 1) and Xe(3P2) with several mercuric and methylmercury halides have been simulated to assign the HgX(B) vibrational distributions. The distributions from the methylmercury halides could be described as Boltzmann types with temperatures ranging from 1000 K for N2(A)+CH3HgI to 9000 K for Xe(3P2)+CH3HgCl. The distributions from the mercuric halides are non‐Boltzmann and the 〈fV〉 are somewhat higher than for the CH3HgX compounds. The initial HgX(B) vibrational distributions are used to discuss the state‐to‐state quenching mechanisms.

The interaction between metastable argon atoms (3P2,0) and krypton atoms has been studied at room temperature using the flowing afterglow technique. Measurements of the emission intensities from the excited‐krypton levels show that only Kr(5p[3/2]2) and Kr(5p[3/2]1) are primary products from Ar* (3P2). The pressure dependence of the emission intensities from other 5p krypton states shows that these are produced by collisional cascade from the 5p[3/2]2,1 levels; some rate constants for these cascade processes are reported. Absorption measurements using the 123.6 nm resonance transition of Kr demonstrate that the emitting Kr(5s 3P1) state carries no excess translational energy; therefore, it must be produced only via radiative cascade from Kr(5p) levels. Thus Ar (3P2) excitation rate constants of 5.6 and 0.65×10−12 cm3 molecule −1⋅sec−1 are established for excitation to Kr(5p[3/2]2) and Kr(5p[3/2]1), respectively. The Ar(3P2)+Kr reaction can serve as a reference for obtaining rate constants for excitation ...

Rate constants and initial HBr and HF product distributions for the title reactions were measured in a fast‐flow apparatus using infrared chemiluminescence techniques. The spectra were interpreted using a new set of Einstein coefficients for HBr, which are listed in the Appendix. The rate constants for HBr(v⩾1) and HF(v⩾1) formation, relative to the H+Cl2 reaction, are 3.3, 0.39, 0.50, 3.4, and 0.003, for Br2, SF5Br, PBr3, SF5, and SF4, respectively. This directly measured Br2 rate constant supports the smaller values that have been estimated in the literature. The initial HBr vibrational distribution (v1:v2:v3:v4:v5=0.03:0.20:0.40:0.31:0.06) from H+Br2 corresponds to 〈fV〉=0.49. The observed HBr vibrational distributions (v1:v2:v3:v4) are 0.28:0.43:0.23:0.06 and 0.63:0.24:0.13 for SF5Br and PBr3, respectively. The SF5Br results are close to the initial distribution and give 〈fV〉=0.36. The low vapor pressure of PBr3 limited the [PBr3] and high [H] was required to observe HBr emission; correcting the observ...

The radiative lifetimes and the collisional deactivation constants by Ne and Ar for all 6p, 6p′, 7p, and 6d states of Xe, except two, were studied by single or two‐photon laser induced fluorescence in the afterglow of a pulsed discharge [the prime symbol denotes the Xe+(2P1/2) core rather than the Xe+(2P3/2) core]. The radiative lifetimes, 30–48 ns for 6p and 6p′ states and 68–172 ns for 7p states, agree well with theoretical values; but, the agreement between experiment and theory is less satisfactory for the 6d states. The collisional deactivation constants for Ne and Ar are similar if there is a nearby product level. However, the deactivation constants by Ar are much larger than for Ne, if there is a large energy defect for the product state. The product distributions also were measured; Ar collisions give products with larger energy defect than collisions with Ne, which tend to favor nearly isoenergetic product states. The number and type of product channels are related to the locations of crossings i...

The OH(v≥0) distributions from the title reactions have been measured in a flowing‐afterglow reactor using infrared chemiluminescence and laser‐induced fluorescence techniques, which give the OH(v≥1) and OH(v≤1) distributions, respectively. The measured OH(v=0) relative population confirmed previous estimates for OH(v=0) populations based on extrapolations of linear surprisals using a three‐body prior. The 〈fV(OH)〉 values closely resemble the 〈fV(HF)〉 and 〈fV(HCl)〉 values from the corresponding F and Cl atom reactions, suggesting similar dynamics for H abstraction by O(3P), F(2P), and Cl(2P) atoms. The room temperature rate constants for OH formation are 4.2±0.5×10−12 (GeH4), 2.1±0.8×10−12 (H2Se), 1.2±0.4×10−12 (SiH4), and ≤3.8×10−14(H2S)cm3 molecule −1 s−1, which are 2–3 orders of magnitude lower than for the corresponding F(2P) and Cl(2P) atom reactions. Formation of OH is not the major product channel from O+PH3; however, for certain conditions there are fast secondary reactions that can lead to strong...

The decay of the CO (a 3Π,v′=0–3) levels have been studied in a flowing‐afterglow apparatus. The vibrational distribution was monitored by observing the CO (a 3Π→X 1Σ+) emission intensity. The results were interpreted to obtain 52.5, 77, and 178 sec−1 for the infrared radiative decay constants for the v′=1, 2, and 3 vibrational levels of CO (a 3Π). The data also establish that the upper limit to the rate constant for vibrational relaxation of CO (a) by collision with He is ?6×10−17 cm3 molecule−1 sec−1, corresponding to a collision probability of ?1.5×10−7.

The relative XeF(B–X) and XeF(C–A) emission intensities from the steady‐state vacuum ultraviolet photolysis of XeF2 have been used to measure the B–C transfer and quenching rate constants of XeF molecules in low vibrational levels. The rare gases N2, CF4, SF6, F2, NF3, CF3H, CF3Cl, HF, CO2, and XeF2 were investigated as buffer gases at room temperature. The transfer rate constants are much larger than the quenching rate constants for He, Ne, Ar, Kr, N2, CF4, and SF6. For Xe, NF3, CHF3, and CClF3 transfer is only 2–4 times faster than quenching and for F2, HF, and CO2 quenching is faster than B–C state transfer. Quenching for XeF(D) was studied for rare gases and for N2. No convincing evidence was found for three‐body quenching by the rare gases and their quenching of the XeF(B, C) and XeF(D) states are reported as two‐body processes for pressures below ∼5 atm. The XeF(D) quenching rate constants are of the same magnitude as the B–C state transfer rate constants. The photochemical and collisional (metastable rare gas atom) dissociative excitation of XeF2 and KrF2 are summarized in the Appendix.

The F atom reactions with NH3, ND3, N2H4, and CH3ND2 were studied by observation of HF and DF infrared chemiluminescence for very short reaction time in a flow reactor at 300 K. Experiments were done for a wide range of reagent and F atom concentrations in order to obtain HF vibrational distributions that were free from contributions of secondary reaction or vibrational relaxation. The HF and DF distributions from NH3, ND3, and CH3ND2 appear to be normal relative to the typical dynamics associated with H abstraction by F atoms and 〈 fV(HF)〉 is 0.40–0.45. The energy disposal to HF by the N2H4 reaction is anomalously low with 〈 fV(HF)〉 being 1/2 of the normal result for H abstraction by F atoms. Such a low 〈 fV〉 has been associated with reactions for which there is considerable radical stabilization energy, and structural calculations in the literature do indicate that there are significant changes in the N2H3 geometry relative to that in N2H4. The HF formation rate constants (300 K) are larger than 1.0×10−...

The radiative decay and collisional deactivation of eight of the ten neutral atomic neon (2p 5 3p) levels have been studied. Neon metastable atoms were generated by a hollow‐cathode discharge in a flowing afterglow apparatus and were optically pumped by a pulsed tunable dye laser to selected p states; the decay rates then were determined as a function of neon pressure from 1–8 Torr by analyzing the decay of spontaneous emission from the excited level. The radiative lifetimes of these eight p states have been measured with an uncertainty of ±3%. These lifetimes were combined with the radiative branching ratios from a given p level to assign absolute transition probabilities for the Ne(3p–3s) transitions. Two‐body deactivation of the Ne(3p) states by collisions with ground state neon atoms have rate constants in the range of 1–5×10−11 cm3 atom−1 sec−1. Intramultiplet relaxation is the dominant quenching mechanism for the p3, p4, p5, p6, p7, and p8 levels. However, for p9 intermultiplet and intramultiplet re...