The lithium superoxide radical: Symmetry breaking phenomena and potential energy surfaces

Comparison of Calculated and Observed Vibrational Frequencies of New Molecules from an Experimental Perspective

“…Also, notice the oxygen-16/oxygen-18 isotopic frequency ratios with lithium 7 computed as 1.0106 and 1.0349 for the symmetric and antisymmetric LiÀO stretching modes, respectively, (B3LYP, for example) illustrate different oxygen participations in these modes, as do the experimental values (1.0100 and 1.0343) [18]. Furthermore, the structural parameters computed in Figure 12.2 are within the range of values presented earlier using a variety of theoretical methods [17], and the OÀLiÀO angle of 44 deduced from isotopic vibrational analysis of the LiO 2 molecule [15] is within approximately a degree of the values calculated here. And the symmetrical structure based on the The chemistry of boron hydrides has been investigated for over a century, and a large number of boron hydride compounds have been identified and characterized; however, aluminum hydride chemistry under normal conditions is limited to the nonvolatile polymeric solid trihydride (AlH 3 ) n [22,23].…”

“…The near agreement of frequencies calculated with the hybrid B3LYP and the pure BPW91 density functionals and the CCSD(T) wavefunction-based methods is reassuring. Frequencies computed at the SCF level are of course higher [17]. We typically find B3LYP values higher than BPW91 values and both slightly higher than observed values owing in part to the neglect of anharmonic corrections [19][20][21].…”

“…A focused, pulsed Nd-YAG laser (1-20 mJ/pulse, 10 Hz) evaporates metal atoms toward the cryogenically cooled window (4 K for hydrogen and neon or 7 K for argon matrix experiments) for codeposition and reaction with pure hydrogen, Ne/reagent, or Ar/reagent gas mixtures. The laser ablation plume not only contains visible light that deduced from infrared and Raman spectra was reaffirmed by subsequent theoretical calculations [15][16][17]. New observations of neon matrix bands at 1093.9, 719.7, and 508.9 cm À1 correlate with the argon matrix 1096.9, 698.8, and 492.4 cm À1 absorptions, respectively, assigned to the ionic LiO 2 molecule [15,18] and with the frequencies recently computed for this molecule (Table 12.1).…”

An IR study of (CO2)n+ (n=3–8) cluster ions in the 1000–3800 cm–1 region

“…These anomalous IR intensities and frequencies may probably be a consequence of symmetry breaking effects occurring in the singlereference methods, such as the Hartree-Fock and the MP2 calculations. [31][32][33][34][35][36] Symmetry breaking effects sometimes predict unreasonably lower-symmetry structures, spurious dipole moments, and unreliable IR intensities and vibrational frequencies. In contrast, since DFT includes electron correlation effects during the optimization of the Kohn-Sham orbitals, the DFT calculations of the C 2 O 4 + ion in this study can avoid the difficulty due to symmetry breaking effects and provide more meaningful results.…”

Note: Is it symmetric or not?

“…Examples of this occur for many systems such as the allyl radical 12,13 (which has unambiguous C 2v symmetry in reality 14 ); a very nice theoretical treatment of the lithium superoxide radical (LiO 2 ) is illustrative in this regard. 15 This "artifactual" symmetry breaking of a molecular structure is a consequence of improper symmetry of the selfconsistent field wavefunction: what Löwdin called the "symmetry dilemma" a half-century ago. 16 This is nothing new -quantum chemists have known about this for a long time -and this is an area which, when encountered, requires careful and thoughtful judgments by computational chemists.…”