Opacity analysis of the H₃ system: Modified rotating‐rod versus Frozen‐Orientation models

The Rotating‐Rod Model is modified to make the adjustable α parameter which appears in the treatment energy dependent. Its predictions for opacity and excitation functions compare well with quasi‐classical H₃ trajectory results, for translational and vibrationalenergy variations and isotopic mass effects. The Frozen‐Orientation Model in its present form is incapable of such an agreement for mass combinations other than H + D₂. It is suggested that the decreaseof α with energy can be interpreted as a transition from adiabatic tosudden behavior, where alignment is only on the average, and much energy isdeposited in the bending modes. This is supported by a correlation between α and the average final rotation.