## 1 Introduction  
L-3_A_-Dibydroxyphenylalanine (Levodopa \(\equiv\) L-Dopa) is a derivative of one of the essential amino acids, phenylalanine. It is an intermediate in dopamine biosynthesis. There are many herbal extracts containing L-dopa. Some high-yielding natural sources include velvet bean (_Mucuna prurviens_ L.) [1] and broad bean (_Vicia fuba_ L.) [2], while other sources include the genera Phanera-Cassia, Canavalia and Dalbergia.  
L-dopa is found to exhibit antioxidant properties which are helpful in the treatment of diseases like cancer, aging, and cardiovascular, neurodegenerative and inflammatory diseases [3, 4]. It is a potent drug for the treatment of neurological disorders like [PERSON]'s disease, characterized by a loss of dopamine in the brain nerve cells. The dopamine molecule cannot cross the blood-brain barrier, whereas L-dopa is able to cross this barrier. Once the L-dopa molecule enters the central nervous system, it is converted into dopamine. As early as 300 BC, Indian Ayurvedic Physicians used to treat [PERSON]'s disease usingthe seeds of velvet bean (_Mucuna pruriens_ L.), which contain 4-6% of L-dopa [5; 6; 7; 8]. It is also useful for food preservation [1; 2].  
The IR and Raman spectra of L-dopa are available without any spectroscopic interpretation or discussion [9; 10]. [PERSON] et al. [11] performed DFT computations at the b3 lyp/6-311g(d,p) level and reported partial interpretations of spectral, conformational, structural and thermodynamic data. [PERSON] et al. [12] experimentally investigated the IR, Raman, UV-vis and \({}^{1}\)H and \({}^{13}\)C NMR spectra and interpreted the spectral data in light of the DFT calculations performed at the b3 lyp/6-31+g(d,p) level. It is to be noted that [PERSON] et al. reported only one conformer, which was of higher energy relative to the lowest-energy conformer C-I. However, [PERSON] et al. reported a total of 12 conformers and interpreted the experimental results with the help of the structure of the higher-energy conformer with respect to the lowest-energy conformer. Furthermore, these authors [11; 12] have only considered the structures in which the H atom of the hydroxyl group of the COOH moiety is directed towards the O atom of the carbonyl (C=O) group, while the present investigation showed that the lowest-energy conformer corresponds to a structure in which the H atom of the hydroxyl group of the COOH moiety is directed towards the N atom of the amino (NH\({}_{2}\)) group.  
The present work deals with the experimental IR, Raman and UV-vis spectra and their analysis in light of the computed spectra and related parameters for the monomeric and dimeric forms of L-dopa using the Gaussian 09, GaussView 5.0 and GAR2 PED software. This paper also contains computations and interpretations of the molecular properties of the lowest-energy conformer of the L-dopa molecule, namely optimized geometrical parameters, possible conformers, barrier heights for different top axes, APT charges, MEP, HOMO-LUMO analysis, thermodynamic functions and bioactive scores. The structure of the molecule plays an important role for many physical and chemical properties of the compound. Thus, the present study is helpful for researchers in the chemical, medicinal and pharmacological fields for understanding these molecular properties. Further, we are planning to synthesize this molecule's new Ln complexes and to investigate their antioxidant activity, which is in accordance with the well-known antioxidant potential of L-dopa. This is in continuation of our ongoing work devoted to the pharmacological activity of lanthanide complexes with biologically active ligands.