Vibrational Relaxation Of HCl Research Articles

Vibrational relaxation of HCl ( v=1) in HCl/CO 2 and HCl/CO 2/argon gaseous mixtures

Vibrational relaxation of HCl( v=1) in HCl/CO 2 and HCl/CO 2/Ar gaseous mixtures has been measured at room temperature (296 K) by the laser-induced fluorescence (LIF) technique. The observed rate constants are smaller than described in the literature. All measured fluorescence curves are successfully recalculated with the rate constants evaluated in this work. Argon as a buffer gas raises the fluorescence intensity, without an influence on the rate constants.

Vibrational relaxation of HCl (ν = 1 – 10) in H 2O [sbnd]HCl(ν) complex-mode collisions

The relaxation of HCl(ν) in H 2O HCl collisions for ν=1–10 is studied using classical trajectory techniques at thermal collision energies. In the presence of strong attraction, the collision partners form a complex, in which intramolecular energy transfer takes place efficiently. For HCl(ν=0–3) many complexes survive for several picoseconds, but for HCl(ν>3) most of the collisions last for about 1 ps or less. On redissociation, the major part of the energy released by HCl(ν) deposits in the HCl rotations. The rest transfers into translation. The extent of vibrational energy transfer increases linearly with increasing ν.

Vibrational relaxation of HCl(v = 1) in HCl/CO/Ar gaseous mixtures between 296 and 173 K

AbstractVibrational relaxation of HCl(v = 1) in HCl/CO/Ar gaseous mixtures has been measured between room temperature and 173 K by the laser‐induced fluorescence (LIF) technique. Rate constants for the total relaxation and the V‐V relaxation have been determined showing that the relaxation is governed by the V‐V process. For the rates of the V‐R,T processes which relax HCl(v = 1) and CO(v = 1) upper limits are given. As in similar systems relaxation efficiency is higher at lower temperatures.

Vibrational relaxation of HCl as a function of xenon density: The role of HCl–Xe complexes

A treatment of the effect of vibrational predissociation of van der Waals complexes on vibrational relaxation rates [Chem. Phys. 29, 253 (1978)] has been extended by including V–V energy transfer between complexed and uncomplexed species and the possibility of different V–T/R relaxation rates for complexed and uncomplexed species. These modifications allow us to reproduce experimentally observed relaxation data for HCl(v=1) over two orders of magnitude in xenon density. The dependence of the vibrational relaxation rate on density is discussed as are the implications of the observed behavior on isolated binary collision formulations of vibrational energy relaxation processes.

Vibrational relaxation of HCl ( v=1) in argon, krypton, and xenon gaseous mixtures between 296 and 173 K

Vibrational relaxation of HCl ( v=1) in Ar, Kr, and Xe has been measured between room temperature and 173 K by the laser-induced fluorescence (LIF) technique. The observed relaxation constants join the high-temperature results from shock tube techniques to the results reported in the solid and liquid phases, thus indicating the possibility of a common relaxation mechanism.

A comparison between the vibrational relaxation rate of HCl in liquid versus supercritical xenon

The vibrational relaxation of HCl has been studied in both liquid Xe at 289 K and supercritical Xe at 291 K. The rate of relaxation of HCl( v = 1) in supercritical Xe is identical to the relaxation rate in the liquid-phase at a common density. These results are consistent with the predictions of an isolated binary collision model for this system. This prediction is valid even if, as expected, HCl—Xe complexes are present in both the liquid and supercritical fluid as long as the nature and concentration of the complexes depend only on density and temperature.

Vibrational relaxation of HCl(v=1) in hydrogen gaseous mixtures at low temperatures

Vibrational relaxation of HCl(v=1) has been measured in mixtures with H2, HD, and D2 in the temperature range between 300 and 140 K using laser-induced fluorescence. Relaxation in mixtures with n-H2 and with hydrogen enriched with its para modification is a pure vibration–translation, rotation (V–T,R) process. In mixtures with HD and D2 both vibration–vibration (V–V) and V–T,R relaxation rates could be determined separately.

Vibrational relaxation of HCl in HCl/Kr and HCl/Xe mixtures

Vibrational relaxation of HCl(v= 1) has been studied in mixtures with Kr and Xe at room temperature with the help of laserinduced fluorescence. Relaxation rate constants of k10(Kr)= 0.3 ± 0.2 and k10(Xe) = 1.1 ± 0.3 Torr−1−1 have been found. The increase in the relaxation efficiency of xenon compared to krypton demonstrates the importance of attractive molecular interactions.

Vibrational relaxation of HCl (v=1, 2, 3) in Ar, Kr, and Xe matrices

The spectroscopy and vibrational relaxation of matrix isolated HC1 (v=1,2,3) have been studied as a function of host (M=Ar, Kr, and Xe) and temperature (9–42 K). FTIR and laser-excited fluorescence excitation spectra were used to determine vibrational frequencies for the v=0−1, 0−2, and 0−3 transitions. The anharmonicity is found to increase relative to the gas phase value with increasing host size and polarizability. Relaxation occurs stepwise, nonradiatively from v=3 to 2, 2 to 1, and 1 to 0. For a given vibrational state, the relaxation rate increases in the series k(Ar)<k(Kr)<k(Xe), i.e., with increasing spectral shift. At 20 K, k10(Ar)=0.9, k10(Kr)=1.2, and k10(Xe)=1.6 ms−1. The deviation from the harmonic approximation, kv,v−1 =vk10, increases in the same sequence with host change. At 20 K, k32/k21/k10=11/4.3/1 for Ar, 53/11/1 for Kr, and 260/33/1 for Xe. These results are in remarkable contrast with those for most other molecules and suggest the importance of an attractive interaction, especially for HC1/Xe, which increases strongly with HC1 bond length. The temperature dependences of the rates are of the same modest magnitude as found in other systems. The smooth trends of rates with vibrational quantum number and host suggest that there are not strong resonances for specific final rotation-local phonon states. Both rotational and translational degrees of freedom probably receive a significant fraction of the vibrational energy transferred.

Vibrational relaxation of HCl in dilute CCl 4 and CCl 3 F solutions

ce:simple-paraicosecond infrared pump, spontaneous anti-Stokes Raman probe experiments determined the vibrational relaxation rates of HCl(ν = 1) dilute in liquid CCl 4 and CCl 3 F at T = 295 K to be (2.12 ± 0.14) × 10 8 s −1 and (1.57± 0.22) × 10 −1 , respectively. If the liquid phase data are interpreted in terms of the isolated binary collision model, the resultant deactivation probabilities are consistent with an extrapolation of gas phase results.

Vibrational relaxation of HCl in HCl/liquid xenon mixtures

The vibrational relaxation of HCl in liquid xenon at −68°C has been studied. Vibrationally excited HCl is created following UV photolysis of HCl. The rate of relaxation of HCl as a function of HCl mole fraction in liquid xenon is the same as the corresponding rate for gas phase HCl at −68°C. Similarly the rate of relaxation of HCl in HClXe collisions is in good agreement with the corresponding gas phase rate. These observations imply that the isolated binary collision model is valid for this system.

Product rotational distribution in the photodissociation of CH 3CF 2Cl

In the laser-induced unimolecular dissociation CH 3CF 2Cl an exceedingly narrow rotational distribution of the HCl product has been observed. The experimental evidence suggests that a few rotations around J = 16 are unusually open channels to either the vibrational relaxation of HCl or the dissociation.The dissociation is investigated in steady state as well as in a thermal beam by far-infrared emission.

Vibrational relaxation of HCl(v = 1) by CO, NO, and O2 and of HBr(v = 1) by CO

The far-from-resonance transfers and the de-excitation processes in HCl–M (M = CO, NO, O2) and HBr–CO systems have been studied by measuring the fluorescence intensity decay rate after laser exciting one then the other of the collision partners. As for the HX–CO (X = Cl or Br) systems, we have thus determined from 300 to 800 K, the rate constant kHX–CO for the energy transfer between the v = 1 vibrational levels of the HX and CO molecules. The rate constant kCOHCl for the V–R, T de-excitation of HCl(v = 1) by CO, as well as limiting values for the other de-excitation rates kCOHBr and kHXCO have also been obtained; these last rates are found to be much smaller then the respective transfer rates kHBr–CO and kCO–HX. As for the systems HCl–NO and HCl–O2, only the sums xHCl–M of the transfer rates kHCl–M and of the de-excitation rates kMHCl have been measured in the same temperature range. The rate constants have been calculated from a semiclassical theory, in which the perturbing potential is a sum of two atom–atom Morse potentials. This theory fails probably because the attractive multipolar interactions are not taken into account.

Chemiluminescence-depletion of vibrational relaxation. Part 2.—HCl(v= 2–4)+ CO2

The chemiluminescence-depletion (c.d.) method has been employed in a study of the relative rates of vibrational relaxation of HCl(v= 2–4) in collisions with CO2. The rate constant k(v→v-1) increases approximately with v2 over the range from v= 1–4. The rotational dependence of the vibrational transfer efficiency, k(v, J→v-1), gives evidence of a decrease toward higher J of the donor molecule.

The vibrational relaxation of HCl(1) by Cl and Br atoms

The vibrational relaxation of HCl(ν = 1) by chlorine and bromine atoms has been measured at 295 K by a discharge flow system using the resonance fluorescence method to detect the halogen atom concentration, combined with laser induced fluorescence. The measured rate constants are: K(HClCl) = (7.0 ± 1.5) × 10 −12 cm 3 molecule −1 s −1, K(HClBr) = (2.6 ± 0.5) × 10 −13 cm 3 molecule −1 s −1.

Vibrational relaxation of HCl(v=1) in the presence of several diatomic molecules at 295–750 °K

The relaxation rates of HCl(v=1) by HF, HBr, H2, D2, N2, and Cl2 have been measured at 295 to 700 °K in shock tube laser-induced fluorescence experiments.

Vibrational relaxation of HCl (v = 1, 2, 3, and 6) by H- and Cl-atoms

Vibrational relaxation of HCl (v = 1, 2, 3, and 6) by H- and Cl-atoms

Vibrational relaxation of HCl(v=1,2,3,6) by H and Cl atoms

Rate coefficients are calculated for the collisional de-excitation of vibrationally excited HCl molecules by H and Cl atoms. Three-dimensional classical trajectories of the collisional dynamics of these reactions are calculated by using London–Eyring–Polanyi–Sato (LEPS) potential-energy surfaces. The results indicate that (1) the rapid deactivation of vibrationally excited HCl by H and Cl atoms can be explained if bound complexes are postulated for both HClH and ClHCl; (2) H- and Cl-atom exchange are efficient mechanisms for relaxing vibrationally excited HCl by Cl and H atoms, respectively; (3) multiple quantum transitions are important in these de-excitation processes; and (4) the major energy transfer processes are vibration to translation in the deactivation of HCl by H atoms and vibration to rotation in the deactivation of HCl by Cl atoms. The vibrational relaxation of HCl by H atoms is faster than vibrational relaxation of HCl by Cl atoms. Room-temperature over-all relaxation rates kv from level v for HCl(v) by H atoms are k2/k1=1.7, k3/k1=2.2, and k6/k1=2.6, where k1=3.0×1013 cm3 mole−1⋅sec−1; for deactivation of HCl(v) by Cl atoms, they are k2/k1=1.7, k3/k1=2.2, and k6/k1 =8.4, where k1=4.5×1012 cm3 mole−1⋅sec−1. For v=1,2, and 3, these over-all rates show a linear dependence with v. The potential-energy wells of 3.8 kcal/mole predicted for the HClH surface and 0.77 kcal/mole predicted for the ClHCl surface have an effect on the collision dynamics corresponding to these surfaces as vibrational energy in the reagent is increased. The collision dynamics on the surface with the deeper potential-energy well are such that the deactivation rate for reaction H+HCl(v=6) shows a much smaller enhancement than that for reaction Cl+HCl(v=6), where the potential-energy well is not as deep. Increased vibrational energy in the reagents does not necessarily enhance the over-all reaction rates in reactions that occur mostly by formation of collision complexes rather than by direct interaction. The results of the calculations are compared with the experimental rates for the de-excitation of HCL (v=1,2,3) by Cl atoms and HCl(v=1) by H atoms. Rate coefficients are provided for many reactions that were not measured experimentally.

Vibrational relaxation of HCl(v=1) by Cl atoms

The vibrational relaxation of HCl(v=1) by Cl atoms at 294°K has been carefully measured by two different techniques. A discharge-flow-tube, laser-fluorescence method yielded a deactivation rate constant kCl = (8.8±2.6) ×10−12 cm3 molecule−1⋅sec−1. A refinement of the uv laser photodissociation method gives a value of kCl = (8±3) ×10−12. The wide ranges of the argon third body pressure and of the HCl pressure show that the process is clearly bimolecular and not termolecular.

Vibrational relaxation of HCl with inert gas collision partners

The vibrational relaxation of HCl has been measured behind incident shock waves in the presence of He, Ne, Ar, and Kr over a temperature range of 800–4100°K and a pressure range of 10–400 torr. The data show a decrease in the efficiency of energy transfer with increasing reduced mass. This tendency appears to be much stronger than predicted by present theories even when the reduced mass is assumed to be that for H atom-inert gas collisions rather than HCl-inert gas.