Vibrational relaxation of highly excited diatomics. I. Method, analysis, and application to HCl(v≤7)+CO2 and N2O

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Abstract
The infrared chemiluminescence method of Smith and co‐workers is adapted to fast flow reactor conditions where a sensitive infrared detector views the vibrationally excited products of various generating reactions through a circularly variable filter in the absence or presence of added quencher molecules. The initial v distributions are found to be totally unrelaxed vibrationally but thermalized rotationally. This allows the experimental measurement of vibrational relaxation rates of high v levels hitherto inaccessible. The modified Stern–Volmer method of analysis is described in detail. Its reference process is the rapid pumping rate constant 3 s−1 out of the field of view. HCl+ is generated by any one of four H atom reactions (with Cl2, ICl, ClNO, or SOCl2) or two Cl atom reactions (with HI or HBr), and its quenching rates by CO2 or N2O are measured. Quenching probabilities from about 5×10−3 to 0.5 per gas‐kinetic collisions for v = 1 to 7 are found for both gases. The results are compared with the limited published data. Detailed discussion is deferred until the following paper which presents data for 18 additional quenchers.

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