John W. Bevan

Rotational‐vibration analysis of the n=0, nν6+ν1−nν6 subband in the hydrogen‐bonded system 16O 12C ⋅⋅⋅ 1H 19F

Thirty‐three P(J) branch and 15 R(J) branch transitions associated with the n=0, nν6+ν1−nν6 vibration in 16O 12C ⋅⋅⋅ 1H 19F have been assigned. Rotational constants B, centrifugal distortion constants DJ, rotational‐vibrational interaction constant α1, and the frequency of the band origin ν0, have been determined as: B″=0.102 148(14)cm−1; B′=0.104 196(14) cm−1; D″J=3.6(1.8)×10−7 cm−1; D″J=3.8 (1.8)×10−7 cm−1; α1=−61.4(5) MHz; ν0=3844.0294 (50) cm−1. The spectrum is consistent with a linear complex having a hydrogen bond ν6 bending frequency of 75±12 cm−1 and excited state r(C⋅⋅⋅F) distance of 3.012 A. A lower limit to the excited state lifetime is set at ≥2.8×10−10 s.

The gas phase infrared spectrum of ν1 and ν1−ν4 HCN‐‐‐HF

A continuously tunable single frequency color center laser has been used to investigate the rovibrational static gas phase infrared spectra of the ν1 (H–F stretching vibration) and its hot bands ν1+ν17 −ν17 and ν1+ν4−ν4 in the linear dimer HCN‐‐‐HF. Observed perturbations in the ν1 and ν1+ν17 −ν17 subbands results from Coriolis interactions of the excited vibrational states ν1 and ν1+ν17 with ν2+2ν4+ν17 and ν2+2ν4+2ν07 , respectively. The influence of Coriolis interactions and vibrationally predissociating excited state lifetimes of 1.06(10)×10−10 s are considered in simulation of the observed band profiles. Molecular and anharmonic cross term parameters associated with investigated vibrational states are also presented. Anharmonic crossterms X○14 , X○17 , and X○47 are evaluated as 8.0252(73), 4.2162(53), and 1.000(49) cm−1, from the available data, including the analysis from the unresolved spectra of ν1−ν4 and ν1−ν4+ν17 −ν17 . The differences of the band origins in ν1 and ν1−ν4 give a value of ν4=168.34...

Preliminary Rovibrational Analysis of the nν6+ν1−nν6 Vibration in HCN⋅⋅⋅HF

A preliminary rotation‐vibration analysis of the n=0 and n=1 subbands associated with the nν6+ν1−nν6 hydrogen‐bonded vibration in HCN⋅⋅⋅HF has been completed. The following excited state rotational constants B′ and band origin frequencies ν0 have been determined for the complex. The results are consistent with a rotation‐vibration interaction constant α1=−68.3±1 MHz which correlates with an excited state r(N⋅⋅⋅F) internuclear distance of 2.762 A, a decrease of 0.034 A relative to the ground state. Excited state lifetimes associated with assigned transitions are demonstrated to be ≥1.8×10−10s while the x16 anharmonic constant is evaluated to be 4.01±0.03 cm−1.

Differentiation of the ground vibrational and global minimum structures in the Ar:HBr intermolecular complex

A fully three-dimensional morphed potential energy surface is reported for Ar:HBr. The morphed potential was obtained from parametrized scaling and shifting transformations of an ab initio potential. The optimum parameters of the morphed potential were determined by a regularized nonlinear least-squares fit to available experimental data. The rovibrational dynamics of the complex were computed using an adiabatic separation of the H–Br intramolecular stretching mode from the intermolecular modes of the system. The ground rovibrational state of the morphed potential was found to have the hydrogen-bound structure Ar–HBr. This state was 10.99 cm−1 more stable than the corresponding state having the van der Waals structure, Ar–BrH, in agreement with experimental data. However, the global minimum of the morphed potential was found to have the van der Waals structure, Ar–BrH. This structure was 20.9 cm−1 lower in energy than the local minimum having the hydrogen-bound structure, Ar–HBr.

Rotational analysis and vibrational predissociation in the ν2 band of HCN dimer

The rovibrational infrared spectrum of the bound C–H stretching vibration, ν2, in the HCN dimer has been analyzed. Observed transition frequencies have been combined with previously recorded microwave data to obtain the following molecular parameters (in cm−1): ν2=3241.5696(8), α2=−0.000 110(1), B‘=0.058 233 92(1), B’=0.058 344(1), D‘J =0.7013(52)×10−7, DJ =0.6636(18)×10−7. The observed full widths at half‐maximum intensity of the observed transitions are consistent with excited state lifetimes of 1.7(4)×10−9 s.

Rovibrational analysis of the v15 band in the HCN---HF hydrogen bonded cluster

Abstract The observation and assignment of rotational structure in the v 1 5 fundamental, the HCN intramolecular bending vibration, of the HCN---HF hydrogen bonded complex is reported, and the rotational constants have been derived. All intramolecular vibrations in this dimer have now been studied, and the frequency shifts of these vibrations upon complex formation have been obtained. The results are compared with the predictions of ab initio molecular orbital calculations.

Rovibrational analysis of ν3 HCN‐‐‐HF using Fourier transform infrared spectroscopy

The gas phase rovibrational spectrum of the ν3 band arising from the C≡N stretching vibration in the hydrogen bonded heterodimer HCN‐‐‐HF has been observed at 0.004 cm−1 instrumental resolution using a Fourier transform infrared spectrophotometer. Analysis of the spectrum gave the following molecular parameters (in cm−1): ν3=2120.935(12), α3=+5.06(19)×10−4, B’=0.119 283(19), D’J=2.30(7)×10−7. Excited state amplitude lifetimes of observed transitions are demonstrated to be 5.6(4)×10−10 s.

Rovibrational analysis of an intermolecular hydrogen‐bonded vibration: The ν16 band of HCN‐‐‐HF

The infrared spectrum of the intermolecular bending vibration, the ν16 band, of the heterodimer HCN‐‐‐HF has been obtained with 0.010 cm−1 resolution, and the rotational structure of this band has been assigned. The spectroscopic constants of the ν16 state in cm−1 are: ν0=550.0285(2); B6=0.117 652 9(10); D6J =0.2791(5)×10−6; q6=0.579(8)×10−4; α6=−0.002 137(1), where the uncertainties cited are one standard deviation.

Molecular Dynamics in Hydrogen‐bonded Interactions: A Preliminary Experimentally Determined Harmonic Stretching Force Field for HCN‐‐‐HF

Observation of the 2ν1 overtone band in the hydrogen‐bonded complex HCN‐‐‐HF permits evaluation of the anharmonicity constant X11=−116.9(1) cm−1 and determination of the anharmonicity corrected fundamental frequency ω1. This information, and available data from previous rovibrational analyses in the common and perdeuterated isotopic species of HCN‐‐‐HF, offer an opportunity for calculation of an approximate stretching harmonic force field. With the assumptions f12=f24=0.0, the remaining force constants (in mdyn/A) are evaluated as: f11=8.600(20), f22=6.228(9), f33=19.115(40), f44=0.2413(39), f13=0.000(13), f14=0.0343(2), f23=−0.211(6), f34=0.000(2). These compare to f11=9.658(2) in the HF monomer and f11=6.244(3) and f33=18.707(16) in the HCN monomer. These results provide the information necessary to quantitatively assess the applicability of the Cummings and Wood approximation in this hydrogen‐bonded complex and also give an estimate of Dej, the equilibrium distortion constant in the harmonic limit. Com...

Determination of dissociation energies and thermal functions of hydrogen‐bond formation using high resolution FTIR spectroscopy

A technique which employs high resolution Fourier transform infrared spectroscopy is demonstrated for evaluation of hydrogen bond dissociation energies D0 and De. Results for HCN‐‐HF give a D0=20.77(22) and De =28.77(45) kJ/mol which are compared with previously determined values obtained from microwave absolute intensity measurements and ab initio molecular orbital calculations. Rovibrational band information available for HCN‐‐HF also permits evaluation of thermal functions of dimer formation in kJ/mol: ΔU○298.2 =20.1(2), ΔH○298.2 =22.6(2), ΔG○298.2 =59.4(2), ΔS○298.2 =−0.1235.