Simply by observing the existence of the Cherenkov radiation from a particle, one can determine its relative velocity with respect to the light speed in medium. Knowing that, one can determine the particle momentum.
It is a ring formed carbon skeleton. The smallest possible cyclic hydrocarbon is cyclopropane (triangular C3H6) together with cyclobutane both being rather unstable (degration to linear propene and 1-butene). Five and six membered rings are quite common.
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon, and thus are group 14 hydrides.