Adverb
By means of a spectroscope
By the analysis of spectra
Source: en.wiktionary.orgAs is observed for most elements, a diatomic scandium hydride has been observed spectroscopically at high temperatures in the gas phase. Source: Internet
Symmetric hydrogen bonds have been observed recently spectroscopically in formic acid at high pressure (>GPa). Source: Internet
Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with its discovery. Source: Internet