J. K. Hancock

Measurement of CO(ν = 1) vibrational energy transfer rates using a frequency‐doubled CO2 laser

Laser‐induced fluorescence studies of CO collisional relaxation have been carried out using the output of a frequency‐doubled, pulsed CO2 laser as a direct source of CO(ν = 1) excitation. Energy transfer cross sections at 298 °K are reported for CO in collisions with He, Ar, H2, D2, N2, O2, Cl2, NO, CH4, CF4, and SF6. The D2–D2 self‐relaxation rate was also obtained from the analysis of CO–D2 mixtures.

Vibrational Deactivation of HF(v=1) in Pure HF and in HF‐Additive Mixtures

The laser‐excited vibrational fluorescence method has been used to obtain room temperature (294±2°K) vibrational relaxation rates for pure HF and in HF‐additive mixtures. Measurement of the quenching of HF(v=1) fluorescence in HF–HF and HF‐additive collisions has yielded the following total deactivation rates: HF†Ar<60 sec−1· torr−1, HF†N2=(1.25 ± 0.6) × 102  sec−1· torr−1, HF†D2=(3.7± 0.4)× 103sec−1· torr−1, HF†H2=(2.4 ± 0.3) × 104sec−1· torr−1, HF†CO2=(5.9± 0.2)× 104 sec−1· torr−1, and HF†H2O≈ HF†D2O=(4.1± 0.5)× 106  sec−1· torr−1. The self‐relaxation rate for HF was found to be HF†HF=(8.74± 0.1)× 104  sec−1 torr−1 in dilute Ar mixtures and also with other additives. A slower rate (4.4± 0.3)× 104 sec−1· torr−1 has been measured in pure HF and is believed to indicate nonequilibrium of the rotational degrees of freedom during self‐relaxation of HF. Observation of 4.3 μ fluorescence from CO2(00°1) and double exponential fluorescent decay from HF–H2 mixtures has led to the following rates for CO2(00°1) and ...

Vibrational deactivation of carbon monoxide by hydrogen and nitrogen from 100 to 650 °K

Collisional quenching of carbon monoxide by hydrogen and nitrogen has been studied in the 100–650°K temperature range using the laser excited vibrational fluorescence method. The rate constant for CO–H2 deactivation increases smoothly with temperature from 2.6±0.3 sec−1·Torr−1 at 112°K to 170±15 sec−1·Torr−1 at 623°K. The vibration‐to‐vibration energy transfer results for CO–N2 mixtures (exothermic direction) show only a slight temperature dependence from 103 to 651°K with a broad maximum of 420±30 sec−1·Torr−1 in the temperature range 300–400°K. Comparison of our rates with high temperature shock tubes results show excellent agreement for the CO–H2 V → R,T process and only fair agreement for the CO–N2 V → V exchange process. This latter discrepancy may be partially due to the uncertainties involved in extracting V → V energy transfer rates from shock tube data.

Vibrational energy transfer in CO2–CO mixtures from 163 to 406 °K

Vibrational energy transfer rates in CO2–CO mixtures have been measured from 163 to 406 °K using the laser excited vibrational fluorescence method. The near resonant V→V transfer step CO(v=1)+CO2(000)ke⇌ke′ CO(v=0)+CO2(001)+ΔE=−206 cm−1 has been measured in the endothermic direction and after detailed balancing [ke′=ke exp(−ΔE/kT)] is in excellent agreement with data taken in the exothermic direction at and above room temperature. V→R,T quenching of the CO2(001) level by CO2 and CO has also been studied. The CO2 self‐relaxation rate reverses in temperature dependence between 250–300 °K with rates becoming progressively faster as temperature decreases. The total quenching rate for CO2 deactivation in CO2–CO collisions behaves similarly to the self‐relaxation rate. It was not possible in the present analysis to separate and distinguish the pathways for V→R,T deactivation in equilibrated CO2–CO mixtures. The cross relaxation terms (CO+2–CO) and (CO+–CO 2) are both expected to be important at low temperatures.

Measurement of the rate of excitation and deactivation of OCS(001), N2O(001), CS2(001), and C2N2(00100) using laser excited CO as a pumping source

The laser fluorescence method has been used to measure CO(ν=1) collisional transfer rates in several binary and ternary gas mixtures at 296°K. Excitation of the CO(ν=1) level was achieved using pulsed 4.6 μm radiation from a frequency doubled CO2 laser. The relative inertness of CO molecules towards V→T deactivation greatly facilitates the study of vibrational relaxation rates of the additive species in selected cases. In this paper, intermolecular V→V transfer rates at 296°K are reported for CO(ν=1) with N2O, OCS, SO2, CS2, C2N2, and for CO(ν=2) with CO. In addition, the additive deactivation rates were determined for the following collisional processes: N2O(001) with N2O, CO, Ar; OCS(001) with OCS, CO, Ar; CS2(001) with CS2, CO; and C2N2(00100) with C2N2 and CO.

Vibrational deactivation of N2O(001) by N2O, CO, and Ar from 144–405 °K

Vibrational deactivation of N2O(001) by N2O, CO, and Ar has been studied from 144 to 405 °K using the laser fluorescence method. The probability of vibration to vibration energy transfer, N2O(001) + CO(v=0) ? N2O(000) + CO(v=1) + ΔE = 81 cm−1, is 0.025 and is independent of temperature from 144 to 405 °K. We have performed theoretical calculations on this rate using the modified Sharma–Brau theory developed by Tam. The present results, together with previous experimental work at higher temperatures, suggest a good theoretical fit above room temperature, but not below. The deactivation of N2O(001) in collisions with N2O, CO, and Ar, N2O(001) + M → N2O(mnl0) + M + ΔE, has been determined to be 102 to 104 times slower than observed for the V→V exchange process. The N2O(001) intramolecular rates become smaller with decreasing temperature with the exception of the N2O self‐relaxation rate. Below 250 °K this rate increases rapidly with decreasing temperature.

Vibrational deactivation rates of HF(ν = 1) by CH4, C2H6, C3H8, C4H10, C3H6, and ClF3

The rates at which vibrationally excited HF is deactivated by CH4, C2H6, C3H8, C4H10, C3H6, and ClF3 have been measured to be (5.3 ± 0.8) × 104; (1.10 ± 0.16) × 105; (1.35 ± 0.2) × 105; (1.7 ± 0.25) × 105; (3.2 ± 0.5) × 105 and (1.13 ± 0.17) × 105 sec−1 · torr−1, respectively, using the laser‐excited vibrational fluorescence technique. It was found that the cross‐section for HF deactivation by the lower alkanes, Cn H2n+2, varied linearly with n. The deactivation rate measured for HF–ClF3 is orders of magnitude greater than has been observed for HF deactivation by other fluorine sources. The importance of the above rate measurements in the understanding and analysis of pulsed HF lasers is discussed in detail.

Temperature‐dependent relaxation of CO(v=1) by HD, D2, and He and of D2(v=1) by D2

Rate constants for the vibrational deactivation of CO in collisions with HD, D2, and He have been measured as a function of temperature using the laser excited vibrational fluorescence technique. Throughout the 109–630 °K range, CO–He and CO–HD samples exhibit a single exponential decay, dominated by V–T,R transfer, with rates increasing rapidly with temperature. Typical collision deactivation rate constants at 630 °K are 22.7 sec−1 torr−1 for He and 82.5 sec−1 torr−1 for HD, and, at 109 °K, 0.067 sec−1 torr−1 for He and 0.27 sec−1 torr−1 for HD. At low temperatures, diffusion and radiative decay become important contributions to the observed rates. In CO–D2 mixtures, double exponential decay of CO fluorescence at large D2 mole fractions is obtained, corresponding to rapid V–V transfer between the (v=1) vibrational levels of CO and D2, followed by coupled V–T,R deactivation. The V–V transfer rate (ΔE=−850 cm−1) increases from 0.26 sec−1 torr−1 at 202 °K to 69.4 sec−1 torr−1 at 633 °K. The V–T,R deactivati...

V–V energy transfer in H2‐additive gas mixtures using a stimulated Raman vibrational fluorescence technique

We report H2 V→V transfer rates to a number of simple molecules using a stimulated Raman vibrational fluorescence technique. The additive gases and respective rate constants (sec−1 torr−1) are HCl(1510±210), DCl(689±30), CO2(497±30), N2O(462±14), HBr(224±18), DBr(212±36), NO(42±17), 12CO(12.3±9.5), and 13CO(9.7±1.9). The ease of experimental data collection, even at total pressures as low as 70 torr, shows the utility and general application of this approach in the excitation of Raman active vibrations in simple systems.

Low‐temperature vibrational relaxation in gaseous deuterium fluoride: Monomer and polymer deactivation effects

Deuterium fluoride vibrational energy transfer measurements have been performed at 198, 209, 232, 264, and 296°K using the laser excited vibrational fluorescence technique. Rate contants for the following processes have been determined: HF(v=1)+DF(v=0) →ke+k12 HF(v=0)+DF(v=1,0) ÷ΔE=1055,3962 cm−1, DF(v=1)+DF(v=0) →k222DF(v=0)+ΔE=2907 cm−1, DF(v=1)+Ar→k2mDF(v=0)+Ar+ΔE=2907 cm−1. Experimental results taken at 198, 209, and 232°K exhibited rate enhancements for increasing DF pressure which is most easily explained as HF(v=1) and DF(v=1) quenching by (DF)n. Relaxation rates in this regime were best described by the empirical equation τ−1=C exp(DPDF), where C and D are temperature dependent coefficients and PDF is the total DF pressure, [DF+(DF)n]. The variation τ−1 with exp(PDF) cannot be reconciled in terms of a monomer–dimer model only. Higher order terms (n=4 and 6) are expected to dominate the collisional quenching of HF(v=1) and DF(v=1). The characterization of (DF)n and its effect upon these studies are...