The MP2/6-31G^** potential energy hypersurface
(PES) of the chemically interesting  molecule ion, C_2H_5^+, 
is analyzed by new procedures proposed by us recently.
The reaction paths start from the minima or saddle points by  
following the so-called reduced gradient procedure and/or its
modification, the tangent search concept, TASC. 

The minimum energy paths (MEP) obtained by TASC are fine approximations 
of those gradient extremals which follow the valley floor (or ridge)
along the smallest (absolute) eigenvalue of the Hessian. 
It is the valley floor gradient extremal which is also termed the 
streambed of the PES.

Tracing the streambed uphill we locate saddle points of the
H-scrambling in C_2H_5^+. 
The potential energy surface of this cation is used to systematically 
explore the properties of reaction path definitions
with particular focus to reaction path bifurcations.
The intrinsic reaction coordinate (IRC) which is mostly used as MEP in 
chemistry, is included for the purpose of comparison.