▁correlation ▁analysis ▁results ▁in ▁two ▁complement ary ▁signals , ▁which ▁referred ▁to ▁as ▁the ▁ 2 D ▁synchron ous ▁and ▁ 2 D ▁asynchronous ▁spectrum . ▁These ▁signals ▁allow ▁amongst ▁others ▁to ▁determine ▁the ▁events ▁that ▁are ▁occurr ing ▁at ▁the ▁same ▁time ▁( in ▁phase ) ▁and ▁those ▁events ▁that ▁are ▁occurr ing ▁at ▁different ▁times ▁( out ▁of ▁phase ) ▁to ▁determine ▁the ▁sequence ▁of ▁spectral ▁changes ▁to ▁identify ▁various ▁inter - ▁and ▁intr am ole cular ▁interactions ▁band ▁assign ments ▁of ▁react ing ▁groups ▁to ▁detect ▁correl ations ▁between ▁spect ra ▁of ▁different ▁techniques , ▁for ▁example ▁near ▁inf ra red ▁spect ro sc opy ▁( N IR ) ▁and ▁Ram an ▁spect ro sc opy ▁ ▁History ▁ 2 D ▁correlation ▁analysis ▁origin ated ▁from ▁ 2 D ▁N MR ▁spect ro sc opy . ▁Is ao ▁N oda ▁developed ▁perturb ation ▁based ▁ 2 D ▁spect ro sc opy ▁in ▁the ▁ 1 9 8 0 s . ▁This ▁technique ▁required ▁sin us oid al ▁perturb ations ▁to ▁the ▁chemical ▁system ▁under ▁investigation . ▁This ▁specific ▁type ▁of ▁the ▁applied ▁perturb ation ▁sever ely ▁limited ▁its ▁possible ▁applications . ▁Following ▁research ▁done ▁by ▁several ▁groups ▁of ▁scient ists , ▁perturb ation ▁based ▁ 2 D ▁spect ro sc opy ▁could ▁be ▁developed ▁to ▁a ▁more ▁extended ▁and ▁generalized ▁bro ader ▁base . ▁Since ▁the ▁development ▁of ▁generalized ▁ 2 D ▁correlation ▁analysis ▁in ▁ 1 9 9 3 ▁based ▁on ▁Fourier ▁transformation ▁of ▁the ▁data , ▁ 2