B. A. Wofford

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.

Rovibrational analysis of the ν71 intermolecular hydrogen bond bending vibration in HCN---HF using far infrared fourier transform spectroscopy

Abstract Static gas phase far infrared Fourier transform spectroscopy has been applied to the observation of the low frequency intermolecular bending fundamental ν 7 1 in the HCN---HF hydrogen-bonded complex. Rovibrational analysis of this band is reported giving the following molecular parameters (in cm −1 ): ν 0 =73.5831(5), B 0 =0.119789(1), D J 0 =2.377(8)×10 −7 , B ν 7 1 = 0.120840 (1), D ν 7 1 , = 2.643 (4) × 10 −7 , q ν 7 1 = 4.248 (4) × 10 −4 . Complications associated with the assignment of such far infrared spectra under equilibrium gas phase conditions are discussed.

Infrared spectrum of the overtone band 2ν05 of the hydrogen bonded complex HCN‐‐‐HF

The infrared spectrum of the overtone of the ‘‘intramolecular’’ bending vibration 2ν05 of the hydrogen bonded complex HCN‐‐‐HF centered at 1437.539 91(24) cm−1 has been obtained with a resolution of 0.006 cm−1. Line assignments for this band as well as two hot bands 2ν05+ν17−ν17 and 2ν05 +2ν27−2ν27 have been made, and rotational constants for all the levels involved have been determined. Despite the fact that the higher J energy levels of the observed lines of 2ν05 are above the dissociation energy of the complex, no predissociative line broadening is apparent.

Predissociating fundamental vibrations of DCN‐‐‐DF

Gas phase rovibrational analysis of ν1, ν2, and ν3 vibrationally predissociating fundamentals arising from D–F, D–C, and C≡N stretching vibrations of DCN–DF are reported. The rotational substructure in these fundamentals and a total of five associated hot bands have been assigned, thus providing precisely determined band origin frequencies, distortion, and rotational constants. The following molecular parameters were determined for the three fundamentals (in cm−1): ν0(ν1)=2730.8909(2), ν0(ν2)=2638.1309(1), ν0(ν3)=1943.0046(3), B0=0.111 807(1), D0J =0.1946(4)×10−6, α1=0.001 449(2), α2=−0.003 00(1), α3=−0.000 399(1). The l‐type doubling constants q‘7 =0.378(3)×10−3 and q7 =0.380(3)×10−3 cm−1 were determined from the observed splitting in ν2+ν17−ν17. Anharmonic cross terms X027 =−0.600(3) and X037 =−0.61(3) cm−1 were also evaluated. Lifetimes of the ν1, ν2, and ν3 excited states were demonstrated to be 5.7(6)×10−10, 5.2(5)×10−9, and 3.0(5)×10−9 s, respectively.

Supersonic molecular beam and static gas phase spectroscopy of intermolecular hot bands associated with ν1 16O12C---1H19F

Abstract Gas phase rovibrational analysis of the ν1 (H stretching vibration) and its associated hot bands ν1+ν3−ν3, ν1 + ν51−ν51 and ν1 + 2ν5, −2ν5 are investigated using a broadband tunable color center laser spectrometer. Rotational and distortion constants associated with the low frequency intermolecular stretching (ν3) and bending (ν51) states are determined to be for ν3:B=0.100786(28) cm−1, DitJ=3.36(30)×10−7 cm−1; and for ν51: B=0.1029736(93) cm−1, DJ=3.598(41)×10−7 cm−1q=0.000235(15) cm−1. The precisely evaluated band origin frequencies permit determination of two anharmonic cross terms associated with the hydrogen bond hypersurface x13 = 8.634(20) and x15 = 5.4099(6) cm−1.