Knowledge Bank

Raman spectra of crystalline polyethylene, $n-C23H48$, and $n-C44H90$ at pressures as high as 40 kbar have been studied at 77 and $298\circ K$ , and five bands characteristic of lattice modes have been observed at various pressures. Each of these bands has been assigned to a lattice mode through symmetry arguments and vibrational analysis of unit cell modes; the pressure dependences of these five lattice frequencies have been calculated and compared with the measured values. Effects of chain folding on the polyethylene spectrum, of end-groups on the spectra of n-paraffins, and of chain length on the lattice frequencies are discussed quantitatively.