A study of alpha-relaxation in ortho-terphenyl by photon correlation spectroscopy

We studied the alpha-relaxation in ortho-terphenyl (OTP) by photon correlat ion spectroscopy (PCS) at temperatures (250 K < T < 270 K) below the crosso ver temperature T-c. We found the following. Contrary to the mode-coupling theory prediction, the non-ergodicity parameter f(c) is temperature indepen dent, which might be due to a strong orientational scattering in OTP. The s tretched exponent beta(k) decreases as temperature decreases, and the relax ation time tau(T) obeys the Vogel-Fulcher law. In the short-time limit of P CS measurement (t similar to 0.1 mu s), no decaying process (neither the Jo hari-Goldstein beta-relaxation nor the critical decay) was observed.