Electron spin resonance investigations of 11B12C, 11B13C, and 10B12C in neon, argon, and krypton matrices at 4 K: Comparison with theoretical results

A matrix isolation ESR and theoretical study of MgN

Matrix isolation experiments have been conducted on the Mg¹⁴N, ²⁵Mg¹⁴N, Mg¹⁵N, and ²⁵Mg¹⁵N radicals which were formed by the reaction of a plume of magnesium metal produced with laser ablation and either acetonitrile vapour or nitrogen atoms. The radicals were isolated in an inert neon matrix at 4.3 K and studied with electron spin resonance spectroscopy. The ground electronic state of MgN was determined to be ⁴Σ^-. The following magnetic parameters were determined experimentally for MgN: g_⊥ = 2.004 78 (2), g_∥ = 2.001 72 (4), |D| = 9797 (6) MHz, A_⊥(¹⁴N) = 19.7 (2) MHz, A_∥ (¹⁴N) = -4.0 (3) MHz, A_⊥(¹⁵N) = 27.5 (3) MHz, A_∥ (¹⁵N) = -5.7 (3) MHz, A_⊥ (²⁵Mg) = -60.7 (5) MHz, and A_∥(²⁵Mg) = -65 (3) MHz. The low-lying electronic states of MgN were also investigated using the complete active space multiconfigurational self-consistent field technique. By plotting the potential energy surface, theoretical parameters for the ground state with a configuration of 5σ²6σ²7σ¹2π¹2π¹ were able to be determined, including r_e = 2.090 Å and D_e = 11.28 kcal/mol.

Calculations of 21 Λ-S and 42 Ω states of BC molecule: Potential energy curves, spectroscopic parameters and spin-orbit coupling effect

The potential energy curves (PECs) were calculated for the 42 Ω states generated from the 21 Λ-S states (X(4)Σ(-), A(4)Π, B(4)Σ(-), a(2)Π, b(2)Σ(-), c(2)Δ, d(2)Σ(+), e(2)Π, 3(2)Π, 4(2)Π, 5(2)Π, 2(2)Σ(-), 3(2)Σ(-), 2(2)Σ(+), 3(2)Σ(+), 2(2)Δ, 3(2)Δ, 1(4)Σ(+), 2(4)Π, 1(4)Δ and 1(2)Φ), which originated from the lowest two dissociation channels, B((2)Pu)+C((3)Pg) and B((2)Pu)+C((1)Dg), of the BC molecule. The PECs were calculated for internuclear separations from 0.08 to 1.10 nm using the CASSCF method, which was followed by the icMRCI approach with the aug-cc-pV6Z basis set. Of these 21 Λ-S states, the e(2)Π, 2(2)Δ, 2(2)Σ(-), 4(2)Π, 1(2)Φ and 3(2)Δ possess the double wells. The A(4)Π, a(2)Π, c(2)Δ, 2(4)Π, 4(2)Π, 5(2)Π, 1(4)Δ and 1(2)Φ states are inverted with the spin-orbit coupling (SOC) effect taken into account. The first well of e(2)Π state and the second well of 4(2)Π and 2(2)Δ states do not have any vibrational states whether with or without the SOC effect included. All the Λ-S and Ω states involved in this paper are bound states. Scalar relativistic correction was included by the third-order Douglas-Kroll Hamiltonian approximation at the level of an aug-cc-pV5Z basis set. Core-valence correlation correction was included at the level of an aug-cc-pCV5Z basis set. The SOC effect was accounted for by the state interaction method with the Breit-Pauli Hamiltonian and the all-electron cc-pCV5Z basis set. The PECs of all the states were extrapolated to the complete basis set limit. The spectroscopic parameters were obtained. The vibrational properties of several Λ-S and Ω states with the relatively shallow wells were evaluated. The SOC effect on the spectroscopic parameters is not obvious for almost all the states. The spectroscopic properties reported in this paper can be expected to be reliably predicted ones.

Optical-optical double resonance, laser induced fluorescence, and revision of the signs of the spin-spin constants of the boron carbide (BC) free radical

The cold boron carbide free radical (BC X (4)Σ(-)) has been produced in a pulsed discharge free jet expansion using a precursor mixture of trimethylborane in high pressure argon. High resolution laser induced fluorescence spectra have been obtained for the B (4)Σ(-)-X (4)Σ(-) and E (4)Π-X (4)Σ(-) band systems of both (11)BC and (10)BC. An optical-optical double resonance (OODR) scheme was implemented to study the finer details of both band systems. This involved pumping a single rotational level of the B state with one laser and then recording the various allowed transitions from the intermediate B state to the final E state with a second laser by monitoring the subsequent E-X ultraviolet fluorescence. In this fashion, we were able to prove unambiguously that, contrary to previous studies, the spin-spin constant λ is negative in the ground state and positive in the B (4)Σ(-) excited state. It has been shown that λ″ < 0 is in fact expected based on a semiempirical second order perturbation theory calculation of the magnitude of the spin-spin constant. The OODR spectra have also been used to validate our assignments of the complex and badly overlapped E (4)Π-X (4)Σ(-) 0-0 and 1-0 bands of (11)BC. The E-X 0-0 band of (10)BC was found to be severely perturbed. The ground state main electron configuration is …3σ(2)4σ(2)5σ(1)1π(2)2π(0) and the derived bond lengths show that there is a 0.03 Å contraction in the B state, due to the promotion of an electron from the 4σ antibonding orbital to the 5σ bonding orbital. In contrast, the bond length elongates by 0.15 Å in the E state, a result of promoting an electron from the 5σ bonding orbital to the 2π antibonding orbitals.

Matrix isolation ESR and theoretical studies of metal phosphides

The ZnP, (67)ZnP, CdP, (111)CdP, and (113)CdP radicals have been formed by laser ablation of the metal with GaP pressed into the metal surface, isolated in an inert neon matrix at 4.3 K and their electronic structure was established using electron spin resonance spectroscopy. The following magnetic parameters were determined experimentally for ZnP/(67)ZnP, g(⊥)=1.9982(2), A(⊥)(P)=111(6) MHz, A(⊥)((67)Zn)=160(2) MHz, and D=-29 988(3) MHz and estimates were made for the following ZnP/(67)ZnP magnetic parameters: g(∥)=1.9941(2), A(∥)(P)=-5(6) MHz, and A(∥)((67)Zn)=180(50) MHz. The following magnetic parameters for CdP/(111)CdP/(113)CdP were determined experimentally: g(⊥)=1.9963(2), A(⊥)(P)=97(3) MHz, A(⊥)((111)Cd)=862(3) MHz, and A(⊥)((113)Cd)=902(3) MHz. Evidence for the formation of the MgP radical was also obtained and an approximate hyperfine coupling constant of A(⊥)(P)=157(6) MHz was determined. The low-lying electronic states of ZnP and MgP were also investigated using the multiconfigurational self-consistent field technique. Potential energy surfaces, binding energies, optimized bond lengths, energy separations, and dissociation energies have been determined. Both radicals are found to have (4)Σ(-) ground states with a leading configuration at r(e) of 10σ(2)11σ(2)5π(1)5π(1)12σ(1) for ZnP and 7σ(2)8σ(2)3π(1)3π(1)9σ(1) for MgP. Significant mixing to this state is calculated for MgP.

Structure and stability of B5C and C5B clusters

Geometry optimizations and vibrational frequencies of B5C and C5B clusters were calculated with the Becke-3LYP method using the 6-311+G(d) basis set and some stable configurations of B5C and C5B clusters have been found. The most stable structure of B5C is a planar six-membered ring. However, for C5B clusters, the most stable structure is linear with a boron atom in position 3. Various configurations of B5C clusters containing three-membered boron rings have predominance in energy, whereas various configurations of C5B clusters containing three-membered carbon rings are disadvantageous in energy. In B5C clusters, isomer2 can be converted into isomer1 by surmounting an energy barrier of 43.83 kJ.mol(-1). In C5B clusters, the conversions of isomer5 into isomer2 and isomer7 into isomer2 have energy barriers of 19.66 and 20.57 kJ.mol(-1), respectively.

Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

The double-aromatic character of selected monocyclic carbon, boron, and borocarbon rings is demonstrated by refined nucleus-independent chemical shift (NICS) analyses involving the contributions of individual canonical MOs and their out-of-plane NICS tensor component (CMO-NICS(zz)). The double aromaticity considered results from two mutually orthogonal Hückel p AO frameworks in a single molecule. The familiar pi orbitals are augmented by the in-plane delocalization of electrons occupying sets of radial (rad) p orbitals. Such double aromaticity is present in B(3) (-), C(6)H(3) (+), C(6) (4+), C(4)B(4) (4+), C(6), C(5)B(2), C(4)B(4), C(2)B(8), B(10) (2-), B(12), C(10), C(9)B(2), C(8)B(4), C(7)B(6), C(6)B(8), and C(14). Monocyclic C(8) and C(12) are doubly antiaromatic, as both the orthogonal pi and radial Hückel sets are paratropic. Planar C(7) and C(9) monocycles have mixed aromatic (pi) and antiaromatic (radial) systems.