Waiting for an actual spectrographer to weigh in, but I think there are databases of molecular emission spectra that can be used to match a sample for complex molecules.
Each element has a known set of emission lines. Mixing elements together in molecules can shift these lines some and add them together. en.wikipedia.org/wiki/Emission_spectrum has some examples across the visible spectrum.
Afaik emission spectra are measured for astronomy and passive remote sensing (since generally you’re just capturing what’s already being emitted). Most spectrometers or spectroradiometers can be used to measure emission or reflection, so then it’s just a question of if you want to measure a sample’s reflectivity by shining a known source of light at it or it’s emission by exciting it with heat or electricity or lasers.
I think Raman spectroscopy is used to excite a crystal lattice with a laser to identify its structure based on the wavelengths emitted outside the laser band, so it has a specific application on crystallography, just like X-ray diffraction.
Also don’t forget mass spectrometers literally rip apart molecules and sort the atoms by mass, so the relative composition of elements can be measured directly.