The molecular ion peak [M]^.+ of an analyte as measured by Electron Ionization Mass Spectrometry has an m/z of 149 and a relative abundance of 100%. The [M].+ has a relative abundance of 6.7% and the [M + 2].+peak has a relative abundance of 5%. The abundance of the major isotope of H, C, N, O, and S are ¹H-100%, ¹²C-98.9%, ¹³C-1.1% , ¹⁴N-99.6%, ¹⁵N-0.4%, ¹⁶O, 99.8%, ¹⁸O-0.2%, ³²S-95.0%, ³³S-0.75% and ³⁴S-4.2%. The most probable molecular formula of the compound is:

Concept:

• ​In the process of ionizing solid or gas phase atoms or molecules, energetic electrons contact with them to produce ions.
• This process is known as electron ionization (EI, formerly known as electron impact ionization and electron bombardment ionization).
• One of the first mass spectrometry ionization methods created was EI.
• The charge number is the quantity of electrons eliminated (for positive ions).
• The horizontal axis in a mass spectrum is stated in units of mass divided by charge number, or m/z.

Conclusion:-

So, The most probable molecular formula of the compound is C5H11NO2S