Mass spectroscopy is not a true spectroscopic technique because the absorption of electromagnetic energy is not involved in any way, although the output from the instrument has all other spectroscopic characteristics.
In this spectroscopic technique, organic molecules are bombarded with electrons and converted to highly energetic positively charged ions, which can break up into smaller ions.
The mass spectrum of a compound can be obtained on a smaller size than for any other of the main spectroscopic techniques.
The principal disadvantage is the destructive nature of the process.