A. A. Stuchebrukhov and R. A. Marcus, Theoretical study of intramolecular vibrational relaxation of acetylenic CH vibration for v= 1 and 2 in large polyatomic molecules (CX_3)_3 YCCH, where X=H or 0 and Y=C or Si, J. Chem. Phys. 98, 6044 (1993).