FT Raman and IR spectra of the crystallized biologically active molecule, 5-Amino-3-methyl-1-phenyl-
1H-pyrazole-4-carbaldehyde (5-APHC, C11H11N3O) have been recorded and analyzed. The equilibrium
geometry, bonding features and harmonic vibrational frequencies of 5-APHC have been investigated with
the help of B3LYP density functional theory (DFT) method with 6-31G(d) and 6-311+G(d,p) as basis set.
The calculated molecular geometry has been compared with the experimental data. The assignments of
the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following
the scaled quantum mechanical force field (SQM) technique. The optimized geometry shows the
co-planarity of the aldehyde group with pyrazole ring. Potential energy surface (PES) scan studies has
also been carried out by ab initio calculations with B3LYP/6-311+G(d,p) basis set. The red shifting of
NH2 stretching wavenumber indicates the formation of N–H  O hydrogen bonding. 1H and 13C NMR
spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were
calculated using the gauge independent atomic orbital (GIAO) method. UV–Vis spectrum of the
compound was recorded in the region 200–400 nm and the electronic properties HOMO and LUMO
energies were calculated by time-dependent TD-DFT approach. Mulliken charges of the 5-APHC molecule
was also calculated and interpreted.