Following the work of Kwak et al. and considering only the excitation sequence where, in a normal-mode factorization of the vibrational wavefunction, the first incident IR pulse induces a one-quantum excitation to a singly excited state and the second IR pulse induces a two-quantum excitation to a doubly excited state in which at least one of the mode indices corresponds to that of the singly excited state, and furthermore assuming temporal disjointedness of these two pulses, the relevant contributions to the third-order nonlinear susceptibility 𝜒 , which is the central quantity for the EVV 2DIR spectral intensities, can by a perturbation-theory development truncated at the first order of anharmonicity in the involved polarization properties (called electrical anharmonicity) and vibrational potential (called mechanical anharmonicity), be expressed as the sum 𝜒 = 𝜒 𝐸 + 𝜒 𝑀 of electrical and mechanical anharmonicity contributions 𝜒 𝐸 and 𝜒 𝑀 , respectively. In the present work, we have ignored the contribution from 𝜒 𝑀 and considered only 𝜒 𝐸 , which we believe will still be sufficient for observations of a qualitative nature. The evaluation of 𝜒 𝐸 involves calculating the relevant vibrational energy levels (of singly and double excited states) and, under the excitation pattern considered, the normal-mode geometric first-and second-order derivatives ( 𝜕𝜇 𝜕𝑄 𝑖