Abstract
ULTRASONIC and spectroscopic techniques have shown that nitric oxide (X2Π) has an abnormally high probability of vibrational relaxation in self collisions at about 300° K. According to Nikitin, the process is electronically non-adiabatic1 because of a resonance between the 1Σ+g state of the vibrationless (NO)2 collision complex and the 3Σ−g state with one NO molecule vibrationally excited. With the point of resonance at a potential energy of about 2.8 kcalories/mole in the 3Σ−g complex, the theory predicts that the probability of relaxation should decrease sharply as the temperature is decreased below 300° K. To test this prediction, we have measured the rate of vibrational relaxation down to 100° K and we find, contrary to the prediction, that the temperature coefficient is negative.
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BILLINGSLEY, J., CALLEAR, A. Negative Temperature Coefficient of the Vibrational Relaxation of Nitric Oxide: an Orientation Effect. Nature 221, 1136–1137 (1969). https://doi.org/10.1038/2211136a0
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DOI: https://doi.org/10.1038/2211136a0
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