CNDO calculation of dipole moment derivatives and infrared intensities of formaldehyde

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Abstract
The complete neglect of differential overlap (CNDO) approximate wavefunctions for formaldehyde have been applied to the calculation of the derivatives of the dipole moment with respect to the symmetry coordinates (∂p/∂Sj). Agreement between the calculated derivatives and the experimental values given by Hisatsune and Eggers for the A1 symmetry species is exceptionally good, permitting an interpretation of the experimental results in terms of electronic distributions in the molecule. The agreement for the B1 and B2 symmetry species is also very good except for the asymmetric in‐plane CH bend. However, the theory successfully predicts that charge reorientation for this motion is quite different from that which occurs in the out‐of‐plane CH bend, so that these motions are represented by CH bond moments of opposite polarity. An analysis is given of the results in terms of derivatives with respect to internal coordinates (∂p/∂rk). Comparison of ∂p/∂rCO values from a series of X2CO molecules (and also with ∂p/∂rCS for X2CS molecules) reveals an interesting trend. An analysis of the various contributions to the calculated ∂p/∂rk values is presented, with an explanation of the calculated results for the out‐of‐plane bending coordinate ∂p/∂γ.
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