Millimeter-Wave Spectra, ab Initio Calculations, and Structures of Fluorophosphane and Chlorophosphane

Ultraviolet photodissociation dynamics of PCl3 at 235 nm: three-dimensional ion imaging and theoretical analysis

The photodissociation dynamics of PCl3 at 235 nm has been studied by monitoring ground state Cl(2P3/2) and spin-orbitally excited Cl(2P1/2) atoms by resonance enhanced multiphoton ionization (REMPI). Also, the PCln+ (n = 0, 1, 2) photoions were observed non-resonantly. The speed distributions and speed-dependent anisotropy parameters β for all these particles have been determined by three-dimensional photofragment ion imaging. The β parameters are close to zero for all these particles. The relative yield of excited Cl(2P1/2) atoms for photodissociation of PCl3 is 0.49 ± 0.03. The speed distributions of Cl(2P3/2) and Cl(2P1/2) atoms are bimodal, mainly resulting from the sequential photodissociation PCl3 → PCl2 → PCl. Near-resonant two-photon ionisation followed by near-resonance one-photon photodissociation is proposed for the production of PCln+ photoions. Using Condon's reflection principle, we constructed the vibrational mode dependent absorption spectrum by accounting for the vibrational motion for all six normal coordinates. As a result, the absorption of 235 nm radiation by PCl3 occurs due to zero vibrational motion rather far from the equilibrium geometry. In particular, movement along the Q2 normal coordinate results in an efficient photoinduced transition into the excited state à of D3h symmetry due to a parallel transition.

Complexes H2 CO:PXH2 and HCO2 H : PXH2 for X=NC, F, Cl, CN, OH, CCH, CH3 , and H: Pnicogen Bonds and Hydrogen Bonds

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate H₂ CO : PXH₂ pnicogen-bonded complexes and HCO₂ H : PXH₂ complexes that are stabilized by pnicogen bonds and hydrogen bonds, with X=NC, F, Cl, CN, OH, CCH, CH₃ , and H. The binding energies of these complexes exhibit a second-order dependence on the O-P distance. DFT-SAPT binding energies correlate linearly with MP2 binding energies. The HCO₂ H : PXH₂ complexes are stabilized by both a pnicogen bond and a hydrogen bond, resulting in greater binding energies for the HCO₂ H : PXH₂ complexes compared to H₂ CO : PXH₂ . Neither the O-P distance across the pnicogen bond nor the O-P distance across the hydrogen bond correlates with the binding energies of these complexes. The nonlinearity of the hydrogen bonds suggests that they are relatively weak bonds, except for complexes in which the substituent X is either CH₃ or H. The pnicogen bond is the more important stabilizing interaction in the HCO₂ H : PXH₂ complexes except when the substituent X is a more electropositive group. EOM-CCSD spin-spin coupling constants ^1p J(O-P) across pnicogen bonds in H₂ CO:PXH₂ and HCO₂ H : PXH₂ complexes increase as the O-P distance decreases, and exhibit a second order dependence on that distance. There is no correlation between ^2h J(O-P) and the O-P distance across the hydrogen bond in the HCO₂ H : PXH₂ complexes. ^2h J(O-P) coupling constants for complexes with X=CH₃ and H have much greater absolute values than anticipated from their O-P distances.

Equilibrium Structures of the Phosphorus Trihalides PF3 and PCl3, and the Phosphoranes PH3F2, PF5, PCl3F2, and PCl5

Among the title species, a reliable and accurate equilibrium geometry ( re structure) is available only for PF3, which has been determined experimentally more than 20 years ago. Here, we report accurate re structures for all title molecules, which were obtained using a composite computational approach based on explicitly correlated coupled-cluster theory (CCSD(T)-F12b) in conjunction with a large correlation-consistent basis set (cc-pCVQZ-F12) to take core-valence electron correlation into account. Additional terms were included to correct for the effects of iterative triple excitations (CCSDT), noniterative quadruple excitations (CCSDT(Q)), and scalar relativistic contributions (DKH2-CCSD(T)). The performance of this computational procedure was established through test calculations on selected small molecules (PH, PF, PCl, PH2, PF2, and PH3). For PF3, PCl3, PH3F2, and PF5 sufficiently accurate experimental ground-state rotational constants from the literature were used to determine semiexperimental re structures, which were found to be in excellent agreement with the corresponding best estimates from the current composite approach. The recommended equilibrium structural parameters are for PCl3, re(PCl) = 203.94 pm and θe(ClPCl) = 100.18°; for PH3F2, re(PHeq) = 138.38 pm and re(PFax) = 164.15 pm; for PF5, re(PFeq) = 153.10 pm and re(PFax) = 157.14 pm; for PCl3F2, re(PCleq) = 200.21 pm and re(PFax) = 159.37 pm; and for PCl5, re(PCleq) = 201.29 pm and re(PClax) = 211.83 pm. The associated uncertainties are estimated to be ±0.10 pm and ±0.10°, respectively.

Complexes between dihydrogen and amine, phosphine, and arsine derivatives. Hydrogen bond versus pnictogen interaction

A theoretical study of the complexes between dihydrogen, H2, and a series of amine, phosphine, and arsine derivatives (ZH3 and ZH2X, with Z = N, P, or As and X = F, Cl, CN, or CH3) has been carried out using ab initio methods (MP2/aug-cc-pVTZ). Three energetic minima configurations have been characterized for each case with the H2 molecule in the proximity of the pnictogen atom (Z). In configuration A, the σ-electrons of H2 interact with σ-hole region of the pnictogen atom generated by the of X-Z bond. These complexes can be ascribed as pnictogen bonded. In configuration C, the lone electron pair of Z acts as the Lewis base, and H2 plays the role of the Lewis acid. Finally, configuration B presents a variety of noncovalent interactions depending on the binary complex considered. The atoms-in-molecules theory (AIM), natural bond orbitals (NBO) method as well as the density functional theory-symmetry adapted perturbation theory (DFT-SAPT) approach were used in this study to deepen the nature of the interactions considered.

Computational tests of quantum chemical models for structures, vibrational frequencies, and heats of formation of molecules with phosphorus and sulfur atoms

The Gaussian-n, complete basis set, and Weizmann-1 quantum chemical models for heats of formation are applied to a set of molecules with relevance to the combustion or pyrolysis of chemical warfare materials. Most of these models generate standard deviations from experiment that are less than 2 kcal/mol. The structures and vibrational frequencies that are generated in the course of these calculations are in good agreement with experimental data. Detailed comparisons with respect to structural types indicate that the present computational models are likely to generate useful data for complex models of combustion and pyrolysis of chemical warfare materials.

Geometry of simple molecules. 2. Modeling the geometry of AX3E and AX2E2 molecules through the nonbonded interaction (NBI) model

A new conceptual model of molecular geometry is presented, called the nonbonded interaction (NBI) model. This model is applied to the geometries of the AX3E and AX2E2 (A = N, O, P, S, As, Se, or Te; X = H, F, Cl, Br, I, CH(3), tBu, CF3, SiH3, Sn(tBu)3, or SnPh3) molecule types. For these molecules, the NBI model can be quantified on the basis of a balance between terminal atom-terminal atom (X-X) interactions and lone pair-terminal atom (E-X) interactions. The empirically observed X-A-X angles range from 91.0 degrees (SeH2) to 180 degrees (O(Sn(tBu)3)2), and the NBI model predicts the X-A-X angle with a mean unsigned error of 1.0 degrees using the empirical A-X distance, 1.5 degrees using the LMP2/6-31G** A-X distance, and 1.1 degrees using the MMFF94 A-X distance. This level of precision compares well to the LMP2/6-31G**-predicted X-A-X angles and is significantly better than the MMFF94-predicted X-A-X angles. Terminal groups that are not sufficiently spherical (CF3, SiH3, and SnPh3) can still be addressed qualitatively by the NBI model, as can molecules with a mixture of terminal groups. The NBI model is able to explain, often quantitatively, the geometry of all of the molecules studied, without any additional postulates or extensive parametrization.

First stretching overtone of BiH3: An extreme local-mode case for XH3-type molecule?

The first stretching overtone region of short-lived, formerly inaccessible BiH3 near 3405 cm(-1) has been measured by Fourier-transform infrared spectroscopy with a resolution of 0.0066 cm(-1). Only the 2nu1(A1)/nu1+nu3(E) band system has been observed. Rotational analysis, with transitions reaching J'max=14, has revealed almost perfect local-mode behavior for the upper states denoted as (200A1/E) in the local-mode notation. Ratios of vibration-rotation interaction parameters q(eff)/alpha(eff)(BB) and r(eff)/alpha(eff)(BC), and the appropriate rotational constant differences, are in good agreement with theoretical local-mode limit values. A simple stretching vibrational model reproduces the observed vibrational term values well, and the potential parameters obtained are close to true values.

Rotational Spectra of the Isotopic Species of Chloroform: Experimental and Ab Initio Structures

The millimeter-wave spectra of three different samples of chloroform (CHCl3, CDCl3, and 13CHCl3) have been measured between 145 and 470 GHz which corresponds to J values between 22 and 70. We report accurate rotational and centrifugal distortion constants for the ground vibrational states of 11 isotopic species. The experimental ro, rs, rIepsilon, rrho<INF POS="STACK">m, and rz structures have been determined using the determined rotational constants. The structure has also been calculated ab initio at the SCF, MP2, RQCISD, and B3LYP levels using triple zeta polarized basis sets. The experimental results are found in excellent agreement with the ab initio predictions. An approximate equilibrium structure has been obtained by combining the experimental results and the ab initio calculations: re(C-H) = 1.080 (2) Å, re(C-Cl) = 1.760 (2) Å, and anglee(HCCl) = 108.23 (2) degrees. Copyright 1998 Academic Press.