An important thing to note about different spectroscopic techniques is that the time an energy scale at which one probes is not always the same as relaxation time of what is being probed. For example, in NMR chemical process such as self-diffusion can be determined even though this occurs at a much slower rate than the probe frequency which is typically in the 100 MHz regime. The plot above is also helpful in illustrating how spectroscopists have covered essentially all of the electromagnetic spectrum as to better understand chemical phenomena.
The energy conversions given below are not that accurate but typically within 1% deviation and easy to remember for the quick calculation to your favorite units. For more precise estimation here is a handy calculator thanks to the Halas Group at Rice University (link). Wikipedia of course has the basics of the electromagnetic spectrum here.