Multimode calculations of rovibrational energies of C2H4 and C2D4

MULTIMODE calculations of low-lying rovibrational energies are reported for C2H4 and C2D4 for total angular momentum J = 0 and 1. The calculations are compared with recent benchmark ones for C2H4 J = 0 [G. Avila and T. Carrington, Jr. J. Chem. Phys. 135, 064101 (2011)] and shown to be highly accurate and roughly two orders of magnitude faster. Calculations of rotation constants for the twelve fundamentals for both C2H4 and C2D4 are reported.