Terahertz Absorption Spectroscopy of Benzamide, Acrylamide, Caprolactam, Salicylamide, and Sulfanilamide in the Solid State

Ye Jiang,Haiyan Wang,He Wang,Jinguang Wu,Xiaodong Wen,Limin Yang,Jia’Er Chen,Fengshan Zhou,Guozhong Zhao,Yanjun Zhai,Kexin Liu

doi:10.1155/2014/732802

Abstract

Terahertz (THz) absorption spectra of the similarly structured molecules with amide groups including benzamide, acrylamide, caprolactam, salicylamide, and sulfanilamide in the solid phase at room temperature and 7.8 K for salicylamide are reported and compared to infrared vibrational spectral calculations using density functional theory. The results of THz absorption spectra show that the molecules have characteristic bands in the region of 0.2–2.6 THz (~7–87 cm−1). THz technique can be used to distinguish different molecules with amide groups. In the THz region benzamide has three bands at 0.83, 1.63, and 1.73 THz; the bands are located at 1.44 and 2.00 THz for acrylamide; the bands at 1.24, 1.66 and 2.12 THz are observed for caprolactam. The absorption bands are located at 1.44, 1.63, and 2.39 THz at room temperature, and at 1.22, 1.46, 1.66, and 2.41 THz at low temperature for salicylamide. The bands at 1.63, 1.78, 2.00, and 2.20 THz appear for sulfanilamide. These bands in the THz region may be related to torsion, rocking, wagging, and other modes of different groups in the molecules.

Highlights

Spectroscopy is a powerful technique for measuring, analyzing, and identifying various molecules
The experimental results indicate that FIR and THz time-domain technique can be effective tools to detect different molecules with amide groups and the bands in the region may be related to torsion, rocking, wagging, and other modes of different groups of the molecules
The FIR spectra of benzamide, acrylamide, caprolactam, and salicylamide were measured using common used Nujol mull method, because mineral oil has no absorption in the far-IR region and the method can protect sample in solid state against wet and avoid distortion of bands or happening of ion exchange

Summary

Introduction

Spectroscopy is a powerful technique for measuring, analyzing, and identifying various molecules. Its utility stems from solid-state compounds and molecules containing low-energy vibrations that, taken as a whole in this region, serve as spectral “fingerprints” usable for their detection and characterization. We have investigated the low-frequency vibrational motions of salicylamide, benzamide, acrylamide, caprolactam, and sulfanilamide in the solid state by concentrating on the spectral region between 7 and 650 cm−1 where crystal lattice vibrations, hydrogen bond bending modes and collective modes, and so forth may occur [26]. The experimental results indicate that FIR and THz time-domain technique can be effective tools to detect different molecules with amide groups and the bands in the region may be related to torsion, rocking, wagging, and other modes of different groups of the molecules

Experimental

Results and Discussion

Conclusions