  We have investigated the spin fluctuations and their interplay with lattice
instabilities in a layered S=1/2 quantum spin system TiOCl. Our Ti and Cl NMR
data demonstrate a pseudo spin-gap behavior below T*=135 K, followed by
successive phase transitions at T_c1=94K and T_c2=66K into the singlet ground
state with an unusually large energy gap E_g=430K. The broad distribution of
the local electric field gradient in the intermediate phase between T_c1 and
T_c2 suggests unconventional spin and lattice (probably orbital) states with an
emerging spin-gap.
