Origin of anomalously long interatomic distances in suspended gold chains. 
The discovery of long bonds in gold atom chains has represented a challenge for physical interpretation.  In fact, interatomic distances frequently attain 3.0-3.6 A values, and distances as large as 5.0 A may be occasionally observed.  Here we studied gold chains by transmission electron microscopy and performed theoretical calculations using cluster ab initio density functional formalism.  We show that the insertion of two carbon atoms is required to account for the longest bonds, while distances above 3 A may be due to a mixture of clean and one C atom contaminated bonds.