In an effort to probe the extent of variations in the interstellar ^ { 7 } Li/ ^ { 6 } Li ratio seen previously , ultra-high-resolution ( R \sim 360,000 ) , high signal-to-noise spectra of stars in the Perseus OB2 and Scorpius OB2 Associations were obtained .
These measurements confirm our earlier findings of an interstellar ^ { 7 } Li/ ^ { 6 } Li ratio of about 2 toward o Per , the value predicted from models of Galactic cosmic ray spallation reactions .
Observations of other nearby stars yield limits consistent with the isotopic ratio \sim 12 seen in carbonaceous chondrite meteorites .
If this ratio originally represented the gas toward o Per , then to decrease the original isotope ratio to its current value an order of magnitude increase in the Li abundance is expected , but is not seen .
The elemental K/Li ratio is not unusual , although Li and K are formed via different nucleosynthetic pathways .
Several proposals to account for the low ^ { 7 } Li/ ^ { 6 } Li ratio were considered , but none seems satisfactory .

Analysis of the Li and K abundances from our survey highlighted two sight lines where depletion effects are prevalent .
There is evidence for enhanced depletion toward X Per , since both abundances are lower by a factor of 4 when compared to other sight lines .
Moreover , a smaller Li/H abundance is observed toward 20 Aql , but the K/H abundance is normal , suggesting enhanced Li depletion ( relative to K ) in this direction .
Our results suggest that the ^ { 7 } Li/ ^ { 6 } Li ratio has not changed significantly during the last 4.5 billion years and that a ratio \sim 12 represents most gas in the solar neighborhood .
In addition , there appears to be a constant stellar contribution of ^ { 7 } Li , indicating that one or two processes dominate its production in the Galaxy .