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The thermal velocity of carbon dioxide is only 3.62% of the Venusian exospheric escape velocity, and the thermal velocity of water vapor is only 5.67%. However, for hydrogen gas, the thermal velocity is 17.02% of the escape velocity. If the thermal velocity for a certain molecule is more than a few percent of the escape velocity, or in this case more than a few hundred meters per second in relation to the escape velocity of 10 km/s, the molecule should have undergone significant loss. Hydrogen gas is nearing 20% of the escape velocity for the Venusian exosphere, and a molecule breaching the threshold of 20% should all be virtually lost via thermal escape after a few billion years, therefore the amount of hydrogen present in the atmosphere of Venus is extremely small.
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