  We report on the results of angle-resolved photoemission experiments on a
quasi-one-dimensional $MX$-chain compound [Ni(chxn)$_2$Br]Br$_2$ (chxn =
1$R$,2$R$-cyclohexanediamine), a one-dimensional Heisenberg system with $S=1/2$
and $J \sim 3600$ K, which shows a gigantic non-linear optical effect. A "band"
having about 500 meV energy dispersion is found in the first half of the
Brillouin zone $(0\le kb/\pi <1/2)$, but disappears at $kb / \pi \sim 1/2$. Two
dispersive features, expected from the spin-charge separation, as have been
observed in other quasi-one-dimensional systems like Sr$_2$CuO$_3$, are not
detected. These characteristic features are well reproduced by the $d$-$p$
chain model calculations with a small charge-transfer energy $\Delta$ compared
with that of one-dimensional Cu-O based compounds. We propose that this smaller
$\Delta$ is the origin of the absence of clear spin- and charge-separation in
the photoemission spectra and strong non-linear optical effect in
[Ni(chxn)$_2$Br]Br$_2$.
