Terahertz Spectroscopy, Amino Acid And Its Vibration Mode

Terahertz (THz) wave,which lies between infrared and microwave in electromagnetic spectrum,belongs to far-infrared band. In the last decade, rapid progress in ultra-fast laser technology provides a steady and reliable optical source for the THz pulses generation,which greatly promotes the research in the THz waveband that is difficult to access before.THz time-domain spectroscopy (THz-TDS), as a newly technique of THz technology, has been widely used in the sensing and imaging field. THz radiation has low photon energies and will not cause harmful photo-ionization in biological tissues. Owing to these advantages, THz-TDS technology is a hot topic for nondestructive sensing in the bio-related fields. Until now this technique has made many significant experimental results in some bio-molecules; the spectrum analysis study in THz range, however, develops incomplete relative to the experiment. Researching adaptive simulation software and methods will help to understand logically the origin of THz spectrum.The main work of this paper is that,we obtained the THz spectra of five amino acids,such as L-methionine and L- threonine ,ascribed and discussed their absorption spectra with experiment and theory simulation.We Obtained their reliable spectra in 0.2-2.8THz by THz-TDS technology. the moleculer structures were download from cambridge structural database ,choose different theories and basis sets such as DFTof Gaussian03,using single and polymolecular conformation to simulate,compare the calculated results and experiment,then with the help of Gaussian View 3.09,we discuss their far-infrared collective vibrational modes. It was found that the absorption peaks are mainly caused by different intramolecular collective vibrational mode,as the frequency higher,the rigidity collective vibrational mode weaker,the group moveing in molecules strengthen.The other work is we select three chlorophyll protein extract from spinach,measure spectrum respond of minim sample with THz-TDS technology. And explore the difference in molecules.This study not only offer references to the application of amino acids and protein,but also useful for mini sample measurement.