Nuclear Quadrupole Hyperfine Structure in HC14N/H14NC and DC15N/D15NC Isomerization: A Diagnostic Tool for Characterizing Vibrational Localization (original) (raw)
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Angewandte Chemie International Edition, 47, 2969 (2008)
The making and breaking of bonds in chemical reactions necessarily involve changes in electronic structure. Therefore, measurements of a carefully chosen electronic property can serve as a marker of progress along a reaction coordinate and provide detailed mechanistic information about the reaction. Herein, we demonstrate through high-resolution spectroscopic measurements and high-level ab initio calculations that nuclear quadrupole hyperfine structure (hfs), an indicator of electronic structure, is highly sensitive to the extent of bending excitation in the prototypical HCNQHNC isomerization system. Thus, measurements of hfs show how the nature of a chemical bond is altered when a vibration that is coupled to the isomerization reaction coordinate is excited.
Laboratory Measurements of the Hyperfine Structure of H 14 N 12 C and D 14 N 12 C
The Astrophysical Journal, 2006
The nuclear quadrupole hyperfine structure of H 14 N 12 C and D 14 N 12 C has been resolved in the laboratory for the first time using millimeter-wave absorption spectroscopy. The transient species were produced in a pulsed DC discharge nozzle, and Doppler broadening effects were minimized by propagating the millimeter waves coaxially with the supersonic molecular beam. New rest frequencies for the , , and J p 1-0 J p 2-1 J p 3-2 rotational transitions of the ground vibrational state were determined. The nuclear quadrupole coupling constants derived from the spectra are kHz for H 14 N 12 C and kHz and (eQq) p 264.5 ע 4.6 (eQq) p 294.7 ע 13.
Monthly Notices of the Royal Astronomical Society
Starting from ab initio electronic structure data, we develop parametrized analytic potential energy surfaces for the HCN and HNC isomers by variationally calculating rovibrational energy levels and adjusting the potential parameters so as to get agreement with experimentally derived transition frequencies to within about 1 cm−1. We also determine an analytic expression in terms of molecular parameters to effortlessly calculate the rovibrational energy levels. We use the obtained empirical potentials to calculate rovibrational levels for eight isotopologues of HCN and eight of HNC up to about 4000 cm−1 above the ground state. The energy levels are estimated to be accurate to within about 3 cm−1 based on comparison to experimental rovibrational transition frequencies for H12C14N, H12C14N, H13C14N, and H12C15N. For all 16 isotopologues, we calculate the zero-point energy and in nine cases we can compare with experimentally derived values. In these comparisons, the variationally obtain...
Chemical Physics Letters, 1995
We report ab initio calculations of the minima and transition states of the HCN ~ HNC isomerization in the X(P~) and A(/~') electronic states, and the A-X transition moment in the neighborhood of the HNC isomer. The HNC(A) potential is fit to a fourth-order Simons-Parr-Finlan force field, and the nuclear coordinate dependence of the A-X transition moment is fit to a polynomial in displacement coordinates. The A-X fluorescence spectrum is calculated using a rigorously calculated wavefunction for the HNC(A), the fitted transition moment, and hundreds of previously calculated HCN/HNC(X) vibrational wavefunctions, which were obtained using a previous global ab initio potential. 0009-2614/95/$09.50
Chemical Physics, 1989
The optothermal detection technique has been used to obtain infrared spectra of the HCN-acetylene complex. In addition to the T-shaped structure observed previously by microwave spectroscopy, a linear isomer also has been discovered and characterized. For both isomers the acetylenic and hydrogen cyanide C-H stretch vibrational bands have been recorded. The results clearly show that the predissociation lifetimes of these isomers depend strongly upon whether or not the C-H vibration excited is involved directly in the formation of the hydrogen bond. Ab initio calculations also have been performed for both isomers at the 6-31G**/MP2 level. Comparisons between these calculations and the experimental results suggest that, for this hydrogen bonded system, an ab initio multidimensional potential surface would be quite realistic. Of particular importance to obtaining a better understanding of the mode dependence of the vibrational predissociation rates is the fact that the calculations reproduce the spectroscopic data which is most sensitive to the coupling between the intramolecular and intermolecular vibrational coordinates.
Astrophysical Journal Supplement Series, 2005
In the present work the J þ 1 J rotational transitions, with J ¼ 0 7, of HC 15 N and the J þ 1 J rotational transitions, with J ¼ 0 7, 9, of DC 15 N have been investigated. The Lamb-dip technique has been employed in order to resolve the hyperfine structure due to deuterium and 15 N. For HC 15 N, the hyperfine parameters have been determined for the first time. With respect to DC 15 N, only the spin rotation of 15 N have been determined for the first time but a more reliable spin rotation of D has been obtained. The experimental evaluation of the hyperfine constants has been aided by highly accurate ab initio computations. Furthermore, the rotational transitions observed allowed us to provide the most accurate ground state rotational parameters known at the moment for both HC 15 N and DC 15 N.
On the structure, lattice energy and 14N nuclear quadrupole coupling constant of solid HCN
Chemical Physics Letters, 1988
The results of electrostatic calculations of the lattice energies of crystals formed from linear hydrogen-bonded chains of HCN molecules are reported. Two types of crystal structures are considered: one in which the chains are aligned with their dipole moments parallel, and the second where alternate chains are aligned antiparallel to each other. The present calculations strongly favour the antiparallel structure, in direct contrast with the parallel structure proposed on the basis of an early X-ray diffraction study. The results of the current calculations are also at variance with those of an earlier lattice energy calculation on the parallel structure. Theoretical estimates of the difference between the gas and solid phase 14N quadrupole coupling constants and hence rms librational amplitudes in solid HCN have been obtained. The results appear to be more consistent with the experimentally observed shifts if the antiparallel structure is assumed.
Re-examination of the hyperfine structure of 14NH2
The Journal of Chemical Physics, 1995
The hyperfine structure of the 14 NH 2 radical is investigated by means of multireference single and double configuration interaction ͑MRCI͒ techniques. Particular attention is paid to the dependence of the coupling constants on the basis set, reference space, and configuration selection energy threshold. It is found that convergence can be obtained only if more than 83 reference configurations are included with an energy threshold of at least 10 Ϫ7 hartree. With up to 126 reference configurations, an energy threshold smaller than 10 Ϫ8 hartree and an uncontracted ͑13s8p2d/8s2p͒ basis set, the MRCI isotropic couplings ͑27.44 and Ϫ68.47 MHz for N and H, respectively͒ are in very good agreement with experimental data ͑27.9 and Ϫ67.2 MHz, respectively͒.
Chemical Physics Letters, 1983
The three pcwblc deuterJtcd species of the lsN-h> drown cl snide dimer hsve been identified by their rotational spec-r1.1 .md rhe following spectroscopic constants have been de:ermined for the vibrationalground states: For D(J'5N...llC'5N: Bo = 1605.6946(l) MHz. DJ = 1.68-1(3) kHz. xD(1) = 162.9(14) LHz; for HC'"N...DC'5N: f3o = 1683.3736(l) MHz, DJ = 1 SSS(SJ Lllz. xD(?) = 175.6(16) hHz: .md for DC'5N...DC'sN: B. = 1604.4947(6) MHz. DJ = 1.64(l) kHz, xD(l) + xD(2) = 36S(_S) kHz. It is concluded that the t\\o monodeuterated species differ in zero-point energy by only a few cm-'_