Knowledge Bank

A large number of lines of all H and D isotapes of the $H3+$ molecular ion have now been assigned. The use of vibration-rotation calculations starting from a good {ab initio} $potential1$ was of great value in assigning many of the lines, particularly those involving higher vibrational and rotational levels. Another good {ab initio} $potential2$ has become available more recently. With slight adjustments to some of the ab initio potential coefficients it is possible to assign many more lines. The present work summarises the potentials obtained by fitting the different isotapes independently, and considers evidence from the isotope effects for the breakdown of the Born-Oppenheimer approximation.