CP Radical Research Articles

Density Functional Theory Guide for an Allyl Monomer Polymerization Mechanism: Photoinduced Radical-Mediated [3 + 2] Cyclization.

Polymerization of allyl ether monomers has previously been considered a free-radical addition polymerization mechanism, but it is difficult to achieve because of the high electron density of their double bond. To interpret the mechanism of photopolymerization, we therefore proposed a radical-mediated cyclization (RMC) reaction, which has been validated by results from quantum chemistry calculations and real-time infrared observation. Our RMC reaction begins with the radical abstracting one allylic hydrogen atom from the methylene group of allyl ether to generate an allyl ether radical with a delocalized π33 bond. Then, the radical reacts with the double bond of a second allyl ether molecule to form a five-membered cyclopentane-like ring (CP) radical. The CP radical abstracts a hydrogen atom from a third ether molecule. At last, a new allyl ether radical is generated and the next circulation as chain propagation begins. The distortion/interaction model was employed to explore the transient state of reaction, and real-time infrared was chosen to clarify the RMC reaction mechanism initiated by different photoinitiators. These results demonstrated that the RMC mechanism can give new insights into these fundamental processes.

Radiative lifetimes of A 2Π, B 2Σ+, a 4Σ+, and b 4Δ states of CP radical

The potential energy curves of X 2Σ+, A 2Π, B 2Σ+, a 4Σ+, and b 4Δ states and their Ω states of CP were calculated using the icMRCI approach. The transition dipole moments between these states were computed. To improve the accuracy of the potential energy curves, core–valence correlation and scalar relativistic corrections were considered. The radiative lifetimes were approximately 10 μs for the A 2Π3/2 and A 2Π1/2 states and 100 ns for the B2Σ+1/2 state; those were approximately 10, 10 – 100, 10, 0.1 – 1, and 10 ms for the a 4Σ+1/2, a 4Σ+3/2, b 4Δ1/2, b 4Δ3/2, and b 4Δ5/2 states, respectively. The spontaneous emissions from the B 2Σ+1/2 – X 2Σ+1/2 system were strong, followed by the A 2Π3/2 – X 2Σ+1/2, A 2Π1/2 – X 2Σ+1/2, B 2Σ+1/2 – A 2Π3/2, and B 2Σ+1/2 – A 2Π1/2 transitions. The strong emissions from the A 2Π3/2 – X 2Σ+1/2 and A 2Π1/2 – X 2Σ+1/2 systems were in the infrared region; those from the B 2Σ+1/2 – X 2Σ+1/2 system were in the visible and ultraviolet regions; and those from the B 2Σ+1/2 – A 2Π3/2, and B 2Σ+1/2 – A 2Π1/2 systems were of visible light. A simple comparison shows that the effect of the spin–orbit coupling on the radiative lifetimes of the A 2Π and B 2Σ+ states was significant. The radiative–lifetime distribution of each level υ versus the rotational quantum number J was evaluated for υ ≤ 15 and J ≤ 70.5.

In search of phosphorus in astronomical environments: The reaction between the CP radical (X2Σ+) and methanimine.

Phosphorus is of particular interest in astrochemistry because it is a biogenic element together with hydrogen, carbon, nitrogen, oxygen, and sulfur. However, the chemical evolution of such element in the interstellar medium (ISM) is still far from an accurate characterization, with the chemistry of P-bearing molecules being poorly understood. To provide a contribution in this direction, we have carried out an accurate investigation of the potential energy surface for the reaction between the CP radical and methanimine (CH2NH), two species already detected in the ISM. In analogy to similar systems, i.e., CH2NH + X, with X = OH, CN, and CCH, this reaction can occur-from an energetic point of view-under the harsh conditions of the ISM. Furthermore, since the major products of the aforementioned reaction, namely, E- and Z-2-phosphanylidyneethan-1-imine (HN=CHCP) and N-(phosphaneylidynemethyl)methanimine (H2C=NCP), have not been spectroscopically characterized yet, some effort has been made for filling this gap by means of accurate computational approaches.

Line lists for the X2Σ+-X2Σ+, A2Π-A2Π and A2Π-X2Σ+ transitions of CP

Rovibrational energy levels of CP are investigated for its X2Σ+ and A2Π electronic states. Rovibronic frequencies observed experimentally for the A2Π-X2Σ+ transition are used to produce empirical energy levels with the MARVEL method (denoted as MARVEL energy levels). The MARVEL energy levels for the X2Σ+ and A2Π states are then employed to fit the empirical potential energy curves (PECs), spin orbit coupling curves (SOCCs) and electronic angular momentum curves (EAMCs) by using the DUO program, also constrained by the corresponding ab initio curves. Meanwhile, empirical Born-Oppenheimer breakdown curves, spin-rotation curves (SRCs), Λ-doubling curves are also added to well reproduce the MARVEL energy levels. These curves referred to as analytical spectroscopic models are as an input to DUO to obtain the fitted energy levels for the X2Σ+ and A2Π states and the line lists for the X2Σ+-X2Σ+, A2Π-A2Π and A2Π-X2Σ+ transitions. Partition functions for temperatures up to 5000 K are computed by using the fitted energy levels and fitted by polynomial expansions. The calculated MARVEL energies can be used for spectroscopic investigations of the interstellar CP radical in various astrophysical sources, especially in circumstellar envelopes and warm clouds. The rovibrational energy levels and line lists derived from the analytical spectroscopic models can be used for predicting spectroscopy at temperatures up to 5000 K for potential applications in related plasmas.

Theoretical study on low-lying electronic states of CP radical: Energy levels, Einstein coefficients, Franck-Condon factors and radiative lifetimes

The state-of-the-art ab initio-based valence internally contracted multireference configuration-interaction (icMRCI) method, including the Davidson correction, core-valence correction and scalar relativistic correction and the basis-set extrapolation, is used to calculate the potential energy curves (PECs) of the X2Σ+, B2Σ+, A2Π, 12Σ−, 12Δ, 22Δ, 22Σ−, 14Σ+, 24Σ+, 14Π, 14Δ, 14Σ−, 24Δ, 24Σ− 16Σ+ and 26Σ+ electronic states for CP radical. We also calculate the transition dipole moments (TDMs), Einstein coefficients and Franck-Condon factors for nineteen dipole allowed transitions between these sixteen states. The PECs are used to fit spectroscopic parameters, which are in excellent agreement with previous experimental and theoretical ones. The computed Franck-Condon factors also agree quite well with accurate semi-empirical results for the A2Π-X2Σ+ and B2Σ+-X2Σ+ systems. Such good agreement implies that the results are accurate enough to assist identification of the spectra from astrophysical sources. Large amounts of energy levels and transition data of high accuracy are provided in this work for CP radical of astrophysical interest, where experimental data are still scarce.

On the formation of phosphorous polycyclic aromatics hydrocarbons (PAPHs) in astrophysical environments.

The formation of phosphorous-containing polycyclic aromatic hydrocarbons (PAPHs) in astrophysical contexts is proposed and analyzed by means of computational methods [B3LYP-D3BJ/ma-def2-TZVPP, MP2-F12, CCSD-F12b and CCSD(T)-F12b levels of theory]. A "bottom-up" approach based on a radical-neutral reaction scheme between acetylene (C2H2) and the CP radical was used investigating: (a) the synthesis of the first PAPH (C5H5P) "phosphinine"; (b) PAPH growth by addition of C2H2 to the C5H4P radical; (c) PAPH synthesis by addition reactions of one CP radical and nC2H2 to a neutral PAH. Results show: (I) the formation of the phosphinine radical has a strong thermodynamic tendency (-133.3 kcal mol-1) and kinetic barriers ≤5.4 kcal mol-1; (II) PAPH growth by nC2H2 addition on the radical phosphinine easily and exothermically produces radicals (1a- or 1-phospha-naphtalenes with kinetic barriers ≤7.1 kcal mol-1 and reaction free energies ≤-102.5 kcal mol-1); (III) the addition of a single CP + nC2H2 to a neutral benzene generates a complex chemistry where the main product is 2-phospha-naphtalene; (IV) because of the CP radical character, its barrierless addition to a PAH produces a resonant stabilized PAPH, becoming excellent candidates for addition reactions with neutral or radical hydrocarbons and PAHs; (V) the same energy trend between all four levels of theory continues a well-calibrated computational protocol to analyze complex organic reactions with astrochemical interest using electronic structure theory.

Infrared spectroscopy of the helium solvated cyclopentadienyl radical in the CH stretch region.

Cyclopentadienyl radicals were produced by vacuum flash pyrolysis and trapped in superfluid helium nanodroplets. The infrared spectrum of the embedded radicals was recorded in the range 3020-3120 cm(-1). Three bands observed at 3056.3, 3086.9, and 3117.3 cm(-1) were assigned to the transitions from the ground state to the three levels of the quadratically Jahn-Teller distorted (i.e., second order Jahn-Teller active) CH stretch vibration with E1' symmetry. Accompanying ab initio calculations showed a vibrationally averaged symmetric equilibrium structure in agreement with the observed vibronic transitions. Our results confirm a symmetric configuration of the cyclopentadienyl (cp) radical that is dynamically Jahn-Teller distorted. Density functional theory calculations and infrared data further suggest that barrier-less reactions of two cp radicals occur within the droplets.

Accurate theoretical spectroscopy of the lowest electronic states of CP radical

The present theoretical calculations on CP X2Σ+, A2Π, 14Σ+, 14Δ, 14Π, 16Π and 16Σ+ electronic states use standard and explicitly correlated coupled cluster approaches, multi-reference configuration interaction (MRCI) techniques in connection with a large panel of basis sets. We also examined core–valence (CV) and scalar relativistic (SR) effects. For the ground electronic state, our calculations reveal that the MRCI+CV+SR method and the coupled cluster technique with perturbative treatment of triple excitations including scalar relativistic effects computed with the Douglas-Kroll approach (RCCSD[T]-DK) in connection with a large basis set lead to an accurate description of CP(X2Σ+). We computed the evolution along the internuclear distance of the diagonal and the off-diagonal spin–orbit integrals between the X2Σ+ and A2Π states. These integrals are then incorporated together with the corresponding potentials into variational treatment of the nuclear motion. We deduced hence the energy positions of the low and high vibronic levels of X2Σ+ and A2Π states. Finally, it is shown the necessity of considering the spin–orbit coupling for accurate prediction of the energy position of these levels.

Extensive ab initio study of the electronic states of CP radical including spin–orbit coupling

The potential energy curves (PECs) of 18 Λ–S states and 13 Ω states generated from six Λ–S states of the CP radical are studied in detail using an ab initio quantum chemical method. All the PEC calculations are performed for internuclear separations from 0.10 to 1.11nm by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification. The spin–orbit (SO) coupling effect is accounted for by the Breit-Pauli Hamiltonian. To discuss the effect on the energy splitting by the core-electron correlations, two all-electron basis sets, cc-pCVTZ and cc-pVTZ, are used for the SO coupling calculations. In order to improve the quality of the PECs, core–valence correlation and scalar relativistic corrections are included. Core–valence correlation corrections are taken into account with a cc-pCVTZ basis set. Scalar relativistic correction calculations are carried out using the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. The spectroscopic parameters of 17 Λ–S bound states and 13 Ω states are calculated. When the core-electron correlations are used to calculate the SO coupling splitting by the all-electron cc-pCVTZ basis set and when the core–valence correlation and scalar relativistic corrections are included in the PECs, the SO coupling splitting energy between the A2Π3/2 and A2Π1/2 Ω states is 153.63cm−1, which agree well with the measurements of 157.87cm−1. Moreover, other spectroscopic parameters are also in excellent agreement with the available experimental ones. It demonstrates that the spectroscopic parameters of 14Σ+, 14Δ, 14Π, 22Π, 16Σ+, 14Σ−, 32Π, 12Δ, 12Σ−, 22Δ, 22Σ−, 24Δ, 24Σ− and 26Σ+ Λ–S states and 13 Ω states reported here can be expected to be reliable predicted ones.

Allyl Radical Nature of a Phenylcyclopentadienyl Radical Annelated with Two Homoadamantene Frameworks

1-Phenylcyclopentadiene fused with two homoadamantene units at the 2,3- and 4,5-positions (4) was deprotonated with KH to lead to the quantitative formation of the corresponding cyclopentadienyl (Cp) anion 3(-). This anion was oxidized by AgCl to afford an orange crystalline solid consisting of Cp radical 3(•) and cyclopentadiene 4. The ESR spectrum in hexane exhibited approximately 15 lines, demonstrating that the two homoadamantene frameworks were equivalent and that the C1-C2(Ph)-C3 moiety of the five-membered ring formed a symmetrical allyl-like radical in agreement with the prediction by DFT calculation. The reaction of the Cp radical 3(•) with an oxygen molecule in the presence of Ag(+)SbF(6)(-) afforded the SbF(6)(-) salt of a phenylpyrylium ion annelated with two homoadamantene frameworks (8(+)SbF(6)(-)).

Accurate potential energy function and spectroscopic study of the X2Σ+, A2Π and B2Σ+ states of the CP radical**Project supported by the National Natural Science Foundation of China (Grant No. 10874064) and the Program for Science & Technology Innovation Talents in Universities of Henan Province in China (Grant No. 2008HASTIT008).

This paper calculates the equilibrium internuclear separations, the harmonic frequencies and the potential energy curves of the X2Σ+, A2Π and B2Σ+ states of the CP radical by the highly accurate valence internally contracted multireference configuration interaction method with correlation-consistent basis sets (aug-cc-pV6Z for C atom and aug-cc-pVQZ for P atom). The potential energy curves are all fitted with the analytic potential energy function by the least-square fitting. Employing the analytic potential energy function, we determine the spectroscopic constants (Be, αe and ωeχe) of these states. For the X2Σ+ state, the obtained values of De, Be, αe, ωeχe, Re and ωe are 5.4831 eV, 0.792119 cm−1, 0.005521 cm−1, 6.89653 cm−1, 0.15683 nm, 12535.11 cm−1, respectively. For the A2Π state, the present values of De, Be, αe, ωeχe, Re and ωe are 4.586 eV, 0.703333 cm−1, 0.005458 cm−1, 6.03398 cm−1, 0.16613 nm, 1057.89 cm−1, respectively. For the B2Σ+ state, the present values of De, Be, αe, ωeχe, Re and ωe are 3.506 eV, 0.677561 cm−1, 0.00603298 cm−1, 5.68809 cm−1, 0.1696 nm, 822.554 cm−1, respectively. For these states, the vibrational states with the rotational quantum number J equals zero (J = 0) are studied by solving the radial nuclear Schrödinger equation using the Numerov method. For each vibrational state, the vibrational level, the classical turning points, the rotational inertial and the centrifugal distortion constants are calculated. Comparison is made with recent theoretical and experimental results.

Predissociation Mechanism and Dynamics of HCP

In the present study, we have observed absorption, fluorescence excitation, and CP radical action spectra of the HCP molecule in the vicinity of the dissociation threshold to H((2)S) + CP(X (2)Sigma(+)). In addition, we have measured the rotational distribution of the CP radical produced from certain single rovibronic levels of the parent HCP molecule. It is found that the CP radical action spectrum starts to appear at the point where the fluorescence intensity decreases suddenly. On the basis of the precise energetic consideration between the parent and the product rovibronic energies, the dissociation energy of HCP to H((2)S) + CP(X (2)Sigma(+)) is determined to be 41 662.3 +/- 0.5 cm(-1). The energy distribution in the predissociation is found to be basically statistical; however, the prominent preferences in the rotational distributions or nonstatistical distributions are observed only when the vibronic energy of the parent level is smaller than the dissociation threshold energy. This preference is qualitatively interpreted by the inefficient energy transfer from the rotational to the vibrational degrees of freedom in the exit region of the X state potential energy surface. As a result, the dissociation proceeds along the linear H-C-P configuration, and this geometrical restriction makes nonstatistical rotational distribution of the CP radical.

CP's Triple-bond Strength Experienced in its THz Spectrum

The submillimeter-wave rotational spectrum of the CP radical in the electronic and vibrational ground state (X2Σ+) was recorded in the frequency region between 572 GHz and 1.05 THz, covering rotational quantum numbers from N = 11 up to 21. The CP radical has been produced by discharging CH4 over red phosphorus buffered with Ar at liquid nitrogen temperature. Analysis of the new rotational data of CP together with those available in the literature allows the derivation of an accurate set of molecular constants, including rotational, B0 = 23859.91521(28) MHz and the centrifugal distortion constant D0 = 39.8140(19) kHz, the fine structure and hyperfine structure parameters. The stiffness of the CP bond can be inferred by requiring only one distortion constant D0 to fit the measured rotational spectrum.

Hydrogen atom transfer reactions of transition-metal hydrides. Kinetics and mechanism of the hydrogenation of .alpha.-cyclopropylstyrene by metal carbonyl hydrides

The hydrogenation of {alpha}-cyclopropylstyrene (CPS) by a series of metal carbonyl hydrides (MH) gives a mixture of the unrearranged hydrogenation product Ph(CH{sub 3})(c-C{sub 3}H{sub 5})CH (UN) and the rearranged hydrogenation product (E)-Ph(CH{sub 3})C{double bond}CHCH{sub 2}CH{sub 3} (RE). With the exception of HCr(CO){sub 3}Cp, second-order kinetics are found, conforming to the rate law {minus}d(CPS)/dt = k(CPS)(MH). The proposed mechanism involves hydrogenation by sequential hydrogen atom transfers from the metal hydride to the organic substrate. The rate-determining step is the first hydrogen atom transfer in which a carbon-centered radical and a metal-centered radical are formed. In the case of HCr(CO){sub 3}Cp at 22{degree}C, the equilibrium constant for this step is K {approximately} 10{sup {minus}12}. The effect of the significant amount of 17-electron {sup {sm bullet}}Cr(CO){sub 3}Cp radical formed in the hydrogenation of CPS by HCr(CO){sub 3}Cp is accommodated by the kinetic analysis. Since the initially formed carbon-centered radical undergoes first-order ring-opening rearrangement in competition with second-order trapping by MH, analysis of the product ratio as a function of (MH) concentration provides relative rates of hydrogen atom transfer from metal hydrides to a carbon-centered radical.

The microwave spectrum of the CP radical and related astronomical search

view Abstract Citations (33) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Microwave Spectrum of the CP Radical and Related Astronomical Search Saito, Shuji ; Yamamoto, Satoshi ; Kawaguchi, Kentarou ; Ohishi, Masatoshi ; Suzuki, Hiroko ; Ishikawa, Shin-Ichi ; Kaifu, Norio Abstract The rotational spectrum of the CP radical was detected in the laboratory by using a source-modulated microwave spectrometer combined with a free space absorption cell. The CP radical was produced by a dc-glow discharge in a mixture of PH3, CH4, and He. Nineteen lines of five rotational transitions were observed in the frequency region of 95-334 GHz and were least-squares analyzed to determine the molecular constants: the rotational constant, the centrifugal distortion constant, the spin-rotation coupling constant, and hyperfine coupling constants for the phosphorus nucleus. Based on the measured and calculated line frequencies, astronomical searches for the interstellar CP radical were made in Orion-KL, Sgr B2, W51A, TMC-1, and IRC + 10216, for which upper limits to the column density were estimated. Publication: The Astrophysical Journal Pub Date: June 1989 DOI: 10.1086/167570 Bibcode: 1989ApJ...341.1114S Keywords: Free Radicals; Interstellar Matter; Microwave Spectra; Molecular Rotation; Carbon; Line Spectra; Phosphorus; Spectrum Analysis; Astrophysics; INTERSTELLAR: MOLECULES; LABORATORY SPECTRA; LINE IDENTIFICATIONS; MOLECULAR PROCESSES full text sources ADS | data products SIMBAD (6)