Blake A. McElmurry

Studies of Ar:HBr using fast scan submillimeter-wave and microwave coaxial pulsed jet spectrometers with sub-kHz precision

Coaxial pulsed jet submillimeter spectra are reported for Ar:H79Br and Ar:H81Br transition frequencies measured with sub-kHz precision. This is confirmed by comparing combination frequency differences associated with ΔF=+/−1 hyperfine components in the rovibrational transitions of the low frequency Σ bending mode with corresponding sum frequencies of the rotational transitions in the ground state precisely measured with a pulsed-nozzle FT microwave spectrometer (1.5 kHz resolution, 200 Hz accuracy). Ground state molecular parameters evaluated using the submillimeter-wave and microwave techniques are demonstrated to have comparable accuracy. Furthermore, excited Σ state molecular constants for the isotopic band origins of Ar:H79Br and Ar:H81Br at 329 611.4284(10) and 329 225.6778(10) MHz are shown to be determined with equivalent accuracy.

Testing the morphed potential of Ar:HBr using frequency and phase stabilized FASSST with a supersonic jet

Abstract The lowest frequency Σ bending vibration of Ar:HBr has been recorded using frequency and phase stabilized Fast Scan Submillimeter Spectroscopic Technique (FASSST) coaxially with a supersonic jet. The fitted band origin was ν 0 =329611.4482(16) MHz, the excited stated rotational constant was B =1236.41359(22) MHz, the distortion constants were D J =0.0124740(36) MHz and H J =−2.503(17)×10 −6 MHz and the quadrupole constants were χ aa =260.9552(79) MHz and D χ =−0.03174(35) MHz for Ar: H 79 Br . Corresponding values have also been determined for the Ar: H 81 Br isotopomer. χ aa and D χ are compared with values predicted from a recently determined morphed potential of Ar:HBr.

The Badger-Bauer rule revisited: correlation of proper blue frequency shifts in the OC hydrogen acceptor with morphed hydrogen bond dissociation energies in OC-HX (X = F, Cl, Br, I, CN, CCH).

Potential morphing has been applied to the investigation of proper blue frequency shifts, Δν0 in CO, the hydrogen acceptor complexing in the hydrogen bonded series OC-HX (X= F, Cl, Br, I, CN, CCH). Linear correlations of morphed hydrogen bonded ground dissociation energies D0 with experimentally determined Δν0 free from matrix and solvent effects demonstrate consistency with original tenets of the Badger-Bauer rule (J. Chem. Phys. 1937, 5, 839-51). A model is developed that provides a basis for explaining the observed linear correlations in the range of systems studied. Furthermore, the generated calibration curve enables prediction of dissociation energies for other related but different complexes. The latter include D0 for H2O-CO, H2S-CO, and CH3OH-CO which are predicted by interpolation and found to be 355(13), 171(11), and 377(14) cm(-1) respectively from available experimentally determined proton acceptor shifts. Results from this study will also be discussed in relation to investigations in which CO has been used as a probe of heme protein active sites.

CMM-RS potential for characterization of the properties of the halogen-bonded OC-Cl2 complex, and a comparison with hydrogen-bonded OC-HCl.

Transitions associated with the vibrations ν₁, ν₁ + ν(b)¹, ν₁ + ν₅¹, and ν₁ + ν₅¹ - ν₅¹ of the complex OC···Cl₂ have been rovibrationally analyzed for several isotopologues involving isotopic substitutions in Cl₂. Spectra were recorded using a recently constructed near-infrared (4.34 to 4.56 μm), quantum-cascade laser spectrometer with cw supersonic slit jet expansion. Spectral analysis allowed precise determination of the ν₅¹ intermolecular vibration of OC-³⁵Cl₂ to be 25.977637(80) cm⁻¹. These results were incorporated with other previously determined data into a spectroscopic database for generation of a five-dimensional morphed potential energy surface. This compound-model morphed potential with radial shifting (CMM-RS) was then used to make more accurate predictions of properties of the OC-³⁵Cl₂ complex including D(e) = 544(5) cm⁻¹, D₀ = 397(5) cm⁻¹, ν₃ = 56.43(4) cm⁻¹, and ν(b)¹ = 85.43(4) cm⁻¹. The CMM-RS potential determined for OC-Cl₂ was also used to compare quantitatively many of the inherent properties of this non-covalent halogen bonded complex with those of the closely related hydrogen-bonded complex OC-HCl, which has a similar dissociation energy D₀. We found that in the ground state, the CO bending amplitude is larger in OC-Cl₂ than in OC-HCl.

A Unified Perspective on the Nature of Bonding in Pairwise Interatomic Interactions

Different classes of ground electronic state pairwise interatomic interactions are referenced to a single canonical potential using explicit transformations. These approaches have been applied to diatomic molecules N2, CO, H2(+), H2, HF, LiH, Mg2, Ca2, O2, the argon dimer, and one-dimensional cuts through multidimensional potentials of OC-HBr, OC-HF, OC-HCCH, OC-HCN, OC-HCl, OC-HI, OC-BrCl, and OC-Cl2 using accurate semiempirically determined interatomic Rydberg-Klein-Rees (RKR) and morphed intermolecular potentials. Different bonding categories are represented in these systems, which vary from van der Waals, halogen bonding, and hydrogen bonding to strongly bound covalent molecules with binding energies covering 3 orders of magnitude from 84.5 to 89,600.6 cm(-1) in ground state dissociation energies. Such approaches were then utilized to give a unified perspective on the nature of bonding in the whole range of diatomic and intermolecular interactions investigated.

A ground state morphed intermolecular potential for the hydrogen bonded and van der Waals isomers in OC:HI and a prediction of an anomalous deuterium isotope effect.

An extended analysis of the noncovalent interaction OC:HI is reported using microwave and infrared supersonic jet spectroscopic techniques. All available spectroscopic data then provide the basis for generating an accurately determined vibrationally complete semiempirical intermolecular potential function using a four-dimensional potential coordinate morphing methodology. These results are consistent with the existence of four bound isomers: OC-HI, OC-IH, CO-HI, and CO-IH. Analysis also leads to unequivocal characterization of the common isotopic ground state as having the OC-HI structure and with the first excited state having the OC-IH structure with an energy of 3.4683(80) cm(-1) above the ground state. The potential is consistent with the following barriers between the pairs of isomers: 382(4) cm(-1) (OC-IH/OC-HI), 294(5) cm(-1) (CO-IH/CO-HI), 324(3) cm(-1) (OC-IH/CO-IH), and 301(2) cm(-1) (OC-HI/CO-HI) defined with respect to each lower minimum. The potential is also determined to have a linear OC-IH van der Waals global equilibrium minimum structure having R(e)=4.180(11) Å, θ(1)=0.00(1)°, and θ(2)=0.00(1)°. This is differentiated from its OC-HI ground state hydrogen bound structure having R(0)=4.895(1) Å, θ(1)=20.48(1)°, and θ(2)=155.213(1)° where the distances are defined between the centers of mass of the monomers and θ(1) and θ(2) as cos(-1)[(1/2)] for i=1 and 2. A fundamentally new molecular phenomenon - ground state isotopic isomerization is proposed based on the generated semiempirical potential. The protonated ground state hydrogen-bonded OC-HI structure is predicted to be converted on deuteration to the corresponding ground state van der Waals OC-ID isomeric structure. This results in a large anomalous isotope effect in which the R(0) center of mass distance between monomeric components changes from 4.895(1) to 4.286(1) Å. Such a proposed isotopic effect is demonstrated to be a consequence of differential zero point energy factors resulting from the shallower nature of hydrogen bonding at a local potential minimum (greater quartic character of the potential) relative to the corresponding van der Waals global minimum. Further consequences of this anomalous deuterium isotope effect are also discussed.

Analysis of the submillimetre Ar:HI Σ bending transition as a test of a morphed potential

Σ bending transitions in the argon:hydrogen–iodide dimer have been analyzed following observation using a frequency and phase stabilized co-axially configured submillimetre supersonic jet spectrometer. This transition is from the ground state Ar–IH isomer to the excited state Ar–HI isomer. Molecular constants with one standard deviation to the fit are determined to be for the ground state: BJ = 1034.08372 (25) MHz, DJ = 10.5962 (77) kHz, HJ = −1.678 (69) Hz, χaa = −1114.4014 (12) MHz, Dχaa = 82.3 (12) kHz. The corresponding constants for the newly determined upper state are: ν0 = 263128.0649 (14) MHz, BJ = 876.47909 (21) MHz, DJ = 5.3692 (52) kHz, HJ = 1.669 (38) Hz, χaa = −535.421 (10) MHz, Dχaa = −106.2 (11) kHz. This data is used to test the accuracy of currently available ab initio and morphed potentials for the complex and to propose refinement of the latter potential.

Paired hydrogen bonds in the hydrogen halide homodimer (HI)2

The HI homodimer was found to have structural and vibrational properties unlike any other previously studied (HX)(2) system, with X = F, Cl, and Br. The infrared spectrum of (HI)(2) is also observed to be distinctly different from the other members of the series. In addition, the interaction energy of the (HI)(2) dimer has been calculated using the coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] level of theory. A four-dimensional morphed intermolecular potential has been generated and then morphed using available near infrared and submillimeter spectroscopic data recorded in supersonic jet expansions. The morphed potential is found to have a single global minimum with a symmetric structure having C(2h) symmetry. The equilibrium dissociation energy is found to be 359 cm(-1) with the geometry in Jacobi coordinates of R(e) = 4.35 Å, θ(1) = 43°, θ(2) = 137°, and φ = 180°. The infrared spectrum is characterized by pairs of excited vibrational states resulting from the coupling of the two HI stretching modes. A qualitative model using a quadratic approximation has been fitted to obtain an estimate of this coupling. Furthermore, a morphed intermolecular potential for the vibrationally excited system was also obtained that gives a quantitative estimate of the shift in the potential due to the excitation. The submillimeter analysis is consistent with a ground state having its highest probability as a paired hydrogen bond configuration with R(0) = 4.56372(1) Å and an average angle θ=cos(-1)((1/2)) = 46.40(1)° (between the diatom center of mass∕center of mass axis and direction of each component hydrogen iodide molecule). On monodeuteration, however, the ground state is predicted to undergo an anomalous structural isotope change to an L-shaped HI-DI structure with highest probability at R(0) = 4.51 Å, θ(1) = 83°, θ(2) = 177°, and φ = 180°. These results provide a test for large scale ab initio calculations and have implications for the interpretation of photoinduced chemistry and other properties of the dimer.

Incorporation of a rovibrational analysis of oc-h2o into 6-d morphed potentials of the complex

LUIS A. RIVERA-RIVERA, SEAN D. SPRINGER, BLAKE A. McELMURRY, Department of Chemistry, Texas A & M University, College Station, TX, USA; IGOR I LEONOV, Microwave Spectroscopy, Institute of Applied Physics, Nizhny Novgorod, Russia; ROBERT R. LUCCHESE, JOHN W. BEVAN, Department of Chemistry, Texas A & M University, College Station, TX, USA; L. H. COUDERT, LISA, CNRS, Universités Paris Est Créteil et Paris Diderot, Créteil, France.

A ROVIBRATIONAL ANALYSIS OF THE WATER BENDING VIBRATION IN OC-H2O AND A MORPHED POTENTIAL OF THE COMPLEX

LUIS A. RIVERA-RIVERA, SEAN D. SPRINGER, BLAKE A. McELMURRY, Department of Chemistry, Texas A & M University, College Station, TX, USA; IGOR I LEONOV, Microwave Spectroscopy, Institute of Applied Physics, Nizhny Novgorod, Russia; ROBERT R. LUCCHESE, JOHN W. BEVAN, Department of Chemistry, Texas A & M University, College Station, TX, USA; L. H. COUDERT, LISA, CNRS, Universités Paris Est Créteil et Paris Diderot, Créteil, France.