  Optical spectra of the 2006 outburst of RS Ophiuchi beginning one day after
discovery to over a year after the outburst are presented here. The spectral
evolution is found to be similar to that in previous outbursts. The early phase
spectra are dominated by hydrogen and helium (I & II) lines. Coronal and
nebular lines appear in the later phases. Emission line widths are found to
narrow with time, which is interpreted as a shock expanding into the red giant
wind. Using the photoionisation code CLOUDY, spectra at nine epochs spanning 14
months after the outburst peak, thus covering a broad range of ionisation and
excitation levels in the ejecta, are modelled. The best-fit model parameters
indicate the presence of a hot white dwarf source with a roughly constant
luminosity of 1.26 x 10^{37} erg/s. During first three months, the abundances
(by number) of He, N, O, Ne, Ar, Fe, Ca, S and Ni are found above solar
abundances; abundances of these elements decreased in the later phase. Also
presented are spectra obtained during quiescence. Photoionisation model of the
quiescence spectrum indicates the presence of a low luminosity accretion disk.
The helium abundance is found to be subsolar at quiescence.
