Molecular-Chain Formation Induced by Infrared-Laser Light Observed in L-Cysteine and Potassium Dihydrogenphosphate

Each of amino acids and phosphate group is capable of forming a chain through repeating dehydration condensation reaction. We have observed Raman scattering spectra of L-cysteine (HSCH2CH(NH2)COOH) and potassium dihydrogenphosphate (KH2PO4 or KDP) before and after irradiation of one pulse of an erbium-doped yttrium aluminum garnet (Er:YAG) laser with its wavelength of 2.94 µm, duration of 0.2 ms, and peak power density of 0.4 MW/cm2. Extra peaks are observed in the spectra after the irradiation, which are not seen in the spectra before the laser irradiation. Comparison of the experimentally obtained spectra with the calculated ones of the chain compounds suggests that the laser light does induce such reactions.