Spin-spin coupling constants in C2H2

We present accurate ab initio calculations of the NMR indirect spin-spin co upling constants of acetylene. Very large basis sets have been used in orde r to ensure near basis-set limit results for the different coupling constan ts, and large CI expansions enable an accurate treatment of electron correl ation effects. The calculated coupling constants are in good agreement with recent experimental estimates of the coupling constants in an isolated ace tylene molecule, corrected for rovibrational effects. The results demonstra te that experiment and theory finally have reached almost the same values f or all the spin-spin coupling constants of the isolated, rigid acetylene mo lecule. (C) 2001 Elsevier Science B.V. All rights reserved.