Amorphous carbon films and CN films were prepared by ion beam deposition using isotopically mass-separated, hyper-thermal (50–400eV) ion species such as 12C2
−, 12C14N− or simultaneous 12C2
− and 14N+ under high vacuum condition. Film properties such as structures, bonding states, compositions, etc. were investigated. The optical band gaps of amorphous carbon films deposited by using 12C2
−ions or CN films deposited by using 12C14N− ions were estimated from optical constants. The gaps were about 2.3eV for the amorphous carbon films and about 0.8 eV for the CN films. Energy dependence of optical constants of CN films formed by simultaneous deposition of C2
− and N+ was investigated. The refractive index (n) and extinction coefficient (k) at λ = 675nm increased 1.5 to 2.4 and 0.3 to 1.3, respectively, with increasing N+ kinetic energy. The relations between bonding states and kinetic energy of hyper-thermal ions are discussed.