wonderder

Why is that the concept of heat or temperature is only related to IR (Infrared Radiations), when the IR are also just like any other EM waves e.g. visible, UV, Radio etc. ? What accounts for the enhanced movement of liquid molecules when they are heated. I can imagine electrons going to a higher energy orbit on being exposed to say IR, but am not able to figure out how the whole molecules can start scurrying around on being heated ?