Structures, Bonding, and Energetics of Potential Triatomic Circumstellar Molecules Containing Group 15 and 16 Elements

Abstract

The recent discovery of PN in the oxygen-rich shell of the supergiant star VY Canis Majoris points to the formation of several triatomic molecules involving oxygen, nitrogen, and phosphorus; these are also intriguing targets for main-group synthetic inorganic chemistry. In this research, high-level ab initio electronic structure computations were conducted on the potential circumstellar molecule OPN and several of its heavier group 15 and 16 congeners (SPN, SePN, TePN, OPP, OPAs, and OPSb). For each congener, four isomers were examined. Optimized geometries were obtained with coupled cluster theory [CCSD(T)] using large Dunning basis sets [aug-cc-pVQZ, aug-cc-pV(Q+d)Z, and aug-cc-pVQZ-PP], and relative energies were determined at the complete basis set limit of CCSDT(Q) from focal point analyses. The linear phosphorus-centered molecules were consistently the lowest in energy of the group 15 congeners by at least 6 kcal mol(-1), resulting from double-triple and single-double bond resonances within the molecule. The linear nitrogen-centered molecules were consistently the lowest in energy of the group 16 congeners by at least 5 kcal mol(-1), due to the electronegative central nitrogen atom encouraging electron delocalization throughout the molecule. For OPN, OPP, and SPN, anharmonic vibrational frequencies and vibrationally corrected rotational constants are predicted; good agreement with available experimental data is observed.

Photochemistry of OPN: Formation of Cyclic PON and Reversible Combination with Carbon Monoxide

“…Extensive quantum chemical calculations on analogous triatomics OPN ( 4 ), P 2 O ( 5 ), N 2 S ( 6 ), SPN ( 7 ), and P 2 S ( 8 ) (Scheme ) suggest that the energy difference between the cyclic and linear forms decreases dramatically with inclusion of heavier atoms. For an instance, cyclic PSN, a 16‐electron triatomic ring bearing two second‐row elements, is merely 4.2 kcal mol −1 above linear SPN (CCSDT(Q)/CBS) . Indeed, it was observed in the photo‐induced isomerization between SPN and SNP .…”

“…According to the Walsh rules, the 16‐electron triatomic rings consisting of at least two first‐row elements, such as cyclic N 2 O, N 2 S, CO 2 , and SiO 2 should be even less stable and synthetically more difficult. As one of the frequently studied candidates, cyclic PON ( 4 , Scheme ) is 29.8 kcal mol −1 (CCSDT(Q)/CBS) higher in energy than OPN . Despite of the moderate barriers associated with the ring‐opening to either OPN (14.8 kcal mol −1 ) or ONP (34.4 kcal mol −1 , B3LYP/6‐311+G(3df)), cyclic PON was not observed in the photoisomerization between OPN and ONP in solid Ar matrix at 16 K…”

“…In addition to the known IR bands of OPN (b, 1464.7 and 1042.9 cm −1 ) and ONP (c, 1788.5, 1749.4, 1718.9, and 864.7 cm −1 ), two weak but distinguishable IR bands at 1109.0 and 869.5 cm −1 appear. The band positions are close to the anharmonic frequencies of 1087 and 870 cm −1 for cyclic PON (d) calculated at the CCSD(T)/ANO2 level …”

“…[a] Calculated anharmonic frequencies and normalized relative intensities (in parentheses) at the CCSD(T)/ANO2 level . [b] Calculated 15 N‐isotopic shifts at the B3LYP/6‐311+G(3df) level.…”

Toward the detection of the triatomic negative ion SPN−: Spectroscopy and potential energy surfaces

“…[18][19][20][21] These species are characterized by large electron affinities (>2 eV) and the ability to readily add electrons. The electronic structure, stability, and spectroscopic parameters of the triatomic ion of S, N, and P have been studied theoretically 22,23 and experimentally. 20 Three isomers, namely, SNP, SPN, and cyc-PSN, have been identified in the a) Author to whom correspondence should be addressed: jfrancisco3@ unl.edu gas phase.…”