But suppose that I kick the rock along the ground, increasing its kinetic energy. Very quickly the rock loses this kinetic energy. So kinetic energy is difficult to store, as a rule. But there are schemes for doing so. For example, you build a large flywheel capable of attaining extremely high rotational speeds. You try to reduce friction (with bearings) to a minimum. This rapidly rotating flywheel is an example of stored kinetic energy. I believe that urban buses have been designed using these kinds of flywheels. The wheels are spun up and then this rotational kinetic energy is transformed into translational kinetic energy (the bus moves forward). But you certainly couldn't store this rotational kinetic energy for nearly as long as the potential energy of the rock on my roof.

So I might use the term "stored energy" when I want to emphasize that it is a lot easier to store potential energy than to store kinetic energy.

The allowed energies of molecules (energy levels) are determined by their structure. According to quantum mechanics, a photon can be absorbed by a molecule only if its energy is about equal to a difference in energy levels. Molecules can have rotational kinetic energy, vibrational kinetic energy, and potential energy resulting from interaction between their constituent atoms. They also can have translational kinetic energy, but this energy is not quantized.

But there are additional rules that come into play when one asks if a particular molecule can absorb (much) infrared radiation. Nitrogen and oxygen, as diatomic gases, and hence don't have the structure that allows for absorption of infrared radiation. In saying this I have to be careful to note that the rules can always be broken, or maybe I should say bent a tiny bit. Nevertheless, it is true that absorption of infrared radiation by nitrogen and oxygen is negligible at least as far as radiation from the atmosphere is concerned. But the triatomic structure of carbon dioxide and water vapor and ozone (as well as methane, composed of 5 atoms) gives them strong infrared absorption bands.

Chemists are very much interested in IR absorption spectra because they are determined by structure, and structure determines function. Two molecules with only slightly different structures can be chemically quite different. Perhaps the most extreme example of this is stereoisomers: molecules identical in every respect except that they are mirror images of each other. And yet they have different properties. Aspartame, an artificial sweetener, is one of four stereoisomers. Of these, one is sweet, one bitter, two tasteless. One isomer of thalidomide is a cure for morning sickness, but its mirror image causes fetal malformation. So it is no wonder that chemists are interested in molecular structure. In a manner of speaking, the only property a molecule has is its structure.