We analyze a time series of optical spectra of SN 1993J-like supernova 1996cb , from 14 days before maximum to 86 days after that , with a parameterized supernova synthetic-spectrum code SYNOW .
Detailed line identification are made through fitting the synthetic spectra to observed ones .
The derived photospheric velocity , decreasing from 11 , 000 { ~ { } km~ { } s ^ { -1 } } to 3 , 000 { ~ { } km~ { } s ^ { -1 } } , gives a rough estimate of the ratio of explosion kinetic energy to ejecta mass , i.e . E / M _ { ej } \sim 0.2 - 0.5 \times 10 ^ { 51 } { ~ { } ergs } / M _ { ej } ( M _ { \sun } ) .
We find that the minimum velocity of hydrogen is \sim 10 , 000 { ~ { } km~ { } s ^ { -1 } } , which suggests a small hydrogen envelope mass of \sim 0.02 - 0.1 ~ { } M _ { ej } , or 0.1 - 0.2 ~ { } M _ { \sun } if E is assumed 1 \times 10 ^ { 51 } { ~ { } ergs } .
A possible Ni ii absorption feature near 4000 { ~ { } \AA } is identified throughout the epochs studied here and is most likely produced by primordial nickel .
Unambiguous Co ii features emerge from 16 days after maximum onward , which suggests that freshly synthesized radioactive material has been mixed outward to a velocity of at least 7 , 000 { ~ { } km~ { } s ^ { -1 } } as a result of hydrodynamical instabilities .
Although our synthetic spectra show that the bulk of the blueshift of [ O i ] \lambda 5577 net emission , as large as \sim 70 { ~ { } \AA } at 9 days after maximum , is attributed to line blending , a still considerable residual \sim 20 { ~ { } \AA } remains till the late phase .
It may be evidence of clumpy or large-scale asymmetric nature of oxygen emission region .