A novel measurement technique has been developed to simultaneously obtain polarized spectra of in-plane (IP) and out-of-plane (OP) vibrational modes in optically thin films deposited on a nonmetallic substrate without using a polarizer. These spectra correspond to the conventional infrared transmission and reflection-absorption (RA) spectra, respectively. It has been commonly believed that the mode-selective measurements require polarizers and a specific surface. In particular, the OP-mode measurements always require a metallic surface to generate the surface-normal electric field in the films. The present technique overcomes the limitations of the measurements by considering the concept of virtual longitudinal-wave light using a new arithmetic regression model. The nonpolarized transmitted infrared ray through thin films on a transparent material (Ge) was collected at different angles of incidence, and the transmittance single-beam spectra were subjected to the chemometric spectral resolution, so that absorbance spectra were finally obtained. The two spectra resolved from the nonpolarization spectra were found to perfectly correspond to the conventional transmission and RA spectra. Since this technique is not affected by the enhancement factor that depends on a dielectric property of the metal surface, the band-intensity ratio of the two resolved spectra can be used for direct evaluation of molecular orientation in the films. Further, band shifts due to TO-LO splitting have clearly been observed on the nonmetallic substrate.