Study of the P₄O₇, P₄O₆S, and P₄O₆Se Vibrational Spectra

Abstract

The theoretical vibrational spectra of P(4)O(6)X (X = O, S, and Se) molecules are determined by employing the Hartree-Fock method in combination with a basis set of double-zeta quality plus polarization functions. A comparison of the three spectra is undertaken, and the shifts of the vibrational frequencies found in the spectra are analyzed. Two effects are considered to explain the changes in the band positions: the mass effect due to the replacement of oxygen by sulfur and selenium, respectively, and the bond strength effect. The mass effect of the substituent is as important as the different bond strengths of the P(V)=X bonds. Previous assignments of the bands in the P(4)O(7) spectrum are also corrected by the theoretical research, and a new correlation among the experimental vibrational spectra of the three compounds is put forth. Newly performed Raman polarization measurements confirm our theoretical findings.

Study of the Geometrical Structure and the Vibrational Spectra of P4O8, P4O6S2, and P4O6Se2

“…An example is the P=X bending mode which was found to be the lowest mode in the vibrational spectra. The energetic position shifted from approximately 255 cm ±1 for P 4 O 7 to 130 cm ±1 for P 4 O 6 Se [8]. Due to the strength of the P=O bond, the P=O stretch mode possesses the highest frequency for P 4 O 7 , while the corresponding P=S stretch mode is only the third highest mode in the P 4 O 6 S vibrational spectra.…”

“…In the present work we used the theoretical methods employed in our previous study [8]. The molecular geometries of P 4 O 8 , P 4 O 6 S 2 , and P 4 O 6 Se 2 were optimized using the SCF procedures employing a DZP basis set given by Scha Èfer [16].…”

“…The molecular geometries of P 4 O 8 , P 4 O 6 S 2 , and P 4 O 6 Se 2 were optimized using the SCF procedures employing a DZP basis set given by Scha Èfer [16]. More details about the basis set can be found in our previous work [8].…”

“…In subsequent work [8] differences in the bonding situation in P 4 O 7 , P 4 O 6 S and P 4 O 6 Se were investigated by analyzing the frequency shifts in the vibrational spectra of these molecules. In this work we could show that the normal modes of the P 4 O 6 bulk remain essentially unchanged from P 4 O 7 to P 4 O 6 S and P 4 O 6 Se.…”

Phosphorene oxides: Bandgap engineering of phosphorene by oxidation

“…For the surface forms (s-P 4 O 2 and s-P 4 O 4 ) in which only dangling oxygens are present, there are indeed no vibrational modes between 500 cm −1 and 1000 cm −1 . In the high frequency region, the vibrational spectrum instead only involves P=O stretching modes; these modes are decoupled from the other vibrations because the P=O bonds are much stronger than P-O bridges, as in the case of the molecular (bulk) phosphorus oxides 49,50 . The P=O stretching modes are separated from the other modes by at least 200 cm −1 for all oxygen concentrations, and there are as many as the number of dangling oxygen in the PO.…”