I am currently studying the textbook Infrared and Raman Spectroscopy by Larkin. In the first chapter of the textbook, the author opens (probably prematurely) with the following statement:
Near-IR spectroscopy measures the broad overtone and combination bands of some of the fundamental vibrations (only the higher frequency modes) and is an excellent technique for rapid, accurate quantitation.
This will likely be covered in later chapters, but the statement piqued my curiosity: For someone who has not yet encountered concepts such as "broad overtone", "combination bands", and "higher frequency modes", what does this all mean? Essentially, I am seeking a brief, but clearer and more elaborate, explanation of what the author has described here.
I would greatly appreciate it if someone who has knowledge of this area would please take the time to clarify.