How Predictable Are IR Transition Moment Directions? Vibrational Transitions in Propene and Deuterated Propenes

Abstract

Transition moment directions of mid-infrared transitions in four isotopomers of propene, CH2CHCH3, CH2CDCH3, CD2CHCD3, and CD2CDCD3, have been determined from linear dichroism spectra recorded in stretched polyethylene as solvent. The results were compared with expectations based on bond directions and with results of ab initio calculations at levels of approximations ranging up to CCSD/6-311G**. The former procedure is found to be unreliable, even for high frequency vibrations. With rare exceptions, the highest levels of ab initio theory agree with the experimental directions to within about ±20°, and for intense transitions, to within the experimental uncertainty of about ±(5−10)°.

Vibrational Transition Moments of Aminopurines: Stretched Film IR Linear Dichroism Measurements and DFT Calculations

“…21 In one case also a strong transition was found to have a polarization that varied between experiment and theory: ν 9 of 9MA is experimentally found to be polarized closely parallel to the orientation axis (51°) but is predicted both in the DFT(B3LYP) and MP2 calculations to have a polarization of about -73°. This vibration has a calculated predominance of ring stretching motion but it has also a considerable contribution of NH 2 scissoring.…”

“…(62) To test the predictive capability of the DFT(B3LYP)/6-31G(d,p) method, we used it on propene and the deuterated propenes which have been investigated both experimentally and computationally by Radziszewski et al 21 We obtained transition energies, IR intensities, and polarizations (Table 6S) very similar to their CCSD/6-311(d,p) results. 21 Although far from conclusive, this indicates that the DFT method is useful in order to get rough estimates of IR moment directions.…”

“…The predictive capability of ab initio methods regarding IR transition moment directions has been evaluted by Radziszewski and co-workers for some small, low-symmetry, organic molecules, including ethylene-d 1 , 20 propene, 21 and s-trans-1,3-butadiene. 22 These studies have shown that correct predictions of IR polarizations are difficult to make and that the convergence of the theoretical results is slow when going toward more sophisticated computatitional methods and that it is necessary to include some of the electron correlation in order to get reliable results.…”

“…DFT(B3LYP)/6-31G(d,p) IR spectra of 7MA, 9MA, and 2A9MP (Tables 3S, 4S, and 5S, respectively). DFT(B3LYP)/6-31G(d,p) IR spectra of the propenes investigated by Radziszewski et al 21 (Table 6S) (7 pages). Ordering information is given on any current masthead page.…”

Understanding at molecular level of nanoporous and co-crystalline materials based on syndiotactic polystyrene

“…The organic molecule is absorbed in the amorphous phases of semicrystalline films of polyethylene or of polyvinylalchool, uniaxially stretched at high draw ratios. This method has been greatly successful and has been applied in several dozens of papers to hundreds of organic molecules [103][104][105][106]. The orientation control of the solute molecules is generally poor and the molecules are assumed to be oriented with their smallest cross section nearly perpendicular to the stretching direction (as schematically shown for indole in Fig.…”