Thermophysical Properties of Tetramethylmethane and Tetramethylsilane Gas Calculated by Means of an Isotropic Temperature-Dependent Potential

An isotropic temperature-dependent potential (ITDP) is calculated for the description of binary iInteractions in gaseous tetramethylmethane, C(CH3)4 , and tetramethylsilane, Si(CH3)4 . The potential parameters of C(CH3)4 and Si(CH3)4 are determined by solving an inverse problem of minimization of the sum of weighted squared relative deviations between experimental and calculated pure gas viscosity (ʹ), second ( pVT)-virial coefficient (B), and second acoustic virial coefficient (;) data. At T=0 K they are obtained for C(CH3)4 and Si(CH3)4 , respectively, as repulsive parameter n=28.02(12) and 20.79(11), equilibrium distance rm=5.7790(30)_10&10 and 5.9051(36)_10&10 m, poten- tial well depth = kB=586.32(42) and 674.75(91) K, and the first excited-level enlargement $=0.0141(3)_10&10 and 0.0188(3)_10&10 m. The influence of the temperature on the potential parameters rm(T) and =(T) is implied in the tem- perature dependence of the effective excited-state enlargement, calculated via the vibrational partition function. The calculated complete sets of normal vibra- tional frequencies for C(CH3)4 and Si(CH3)4 are consistent with the available experimental data. In addition, good agreement is observed between the calcula- tions and new Raman spectroscopic measurements on C(CH3)4 . Tables for recommended thermophysical properties (B, ʹ, and self-diffusion \D) and effective 1439 0195-928X 00 1100-1439 18.00 0 2000 Plenum Publishing Corporation 1 Institute of Electronics BAS, 72 Tzarigradsko chaussee, 1784 Sofia, Bulgaria. 2 To whom correspondence should be addressed. E-mail: Lydia ie.bas.bg. 3 Institut fu r Physikalische und Theoretische Chemie, Hans-Sommer Strasse 10, D-38106 Braunschweig, Germany. 4 Institute of Chemical Engineering and High Temperature Chemical Processes, P.O. Box 1414, GR-26500 Patras, Greece. 5 Lucent Technologies, 101 Crawfords Corner Road, Holmdel, New Jersey 07733, U.S.A.