Showing papers by "Rodney S. Ruoff published in 1988"

Rotational spectrum and structure of the linear HCN trimer

Abstract: Microwave rotational spectra have been observed for 22 isotopic species of an HCN, hydrogen‐bonded trimer with the pulsed nozzle, Fourier transform method using the Flygare/Balle Mark II spectrometer. The 14N nuclear quadrupole hyperfine structure was analyzed and the interaction constants and line centers determined. The line centers were fitted to obtain ground vibronic state rotational constants. For the normal isotopic species of (HCN)3, B0 was found to be 469.3073(1) MHz and DJ, 82.6(1) Hz. The quadrupole coupling constants χ(n) are −4.049(2), −4.251(2), and −4.375(1)MHz for n=1, 2, and 3, respectively, in HCN(1)HCN(2)HCN(3). The trimer has a linear or very near linear equilibrium structure. The B0’s are insensitive to the position and torsional oscillations of the central HCN but they determine the outer HCNs quite accurately. An isotopic substitution method gives R, the c.m. distance between the outer HCN’s, to be 8.790 A in the 14–14–14 species. A slightly smaller value 8.788 A is obtained from a ...

Rotational spectra and structures of small clusters: The Ar4–H/DF pentamers

Abstract: The 40Ar4–HF and –DF clusters have been identified and characterized by their microwave rotational spectra using a Flygare–Balle FT spectrometer with a pulsed supersonic nozzle to generate and detect the clusters. The observed J=2→3 to 6→7 transitions have fine structure limited to K=0, ±3 and ±6, indicative of symmetric tops with a threefold axis of symmetry produced by I=0 nuclei. For Ar4–HF the rotational constants B0, DJ, and DJK are 623.4539(1) MHz, 1.062(1) kHz, and 0.611(31) kHz, respectively; and for Ar4–DF, 618.5846(1) MHz, 1.030(1) kHz, and 0.665(4) kHz. The results show that the clusters consist of the trigonal Ar3–H/DF tetramer reported earlier, with a fourth argon on the back side of the Ar3 group to form a tetrahedral or near tetrahedral Ar4. In both clusters the H/DF lies along the threefold axis of the Ar3 group, with the H/D end pointed at its face. If one assumes an Ar–Ar distance of 3.85 A for both clusters, the Ar3 plane to HF c.m. distance for Ar4–HF with a tetrahedral Ar4 is 2.713 A ...

Rotational spectra and structures of small clusters containing the HCN dimer: (HCN)2–Ar, a T‐shaped trimer

Abstract: Microwave rotational spectra have been observed for the four 14N/15N isotopic species of an (HCN)2–Ar trimer with the pulsed nozzle Fourier transform method using the Flygare Mark II spectrometer. Thirteen J→J’ asymmetric top transitions were measured in the 2.5 to 10 GHz region for the parent 14N,14N trimer and nine for each of the other three species. The 14N nuclear quadrupole hyperfine structure was analyzed for the transitions and the interaction constants and line centers determined. The line centers were fitted to obtain ground vibronic state rotational and quartic centrifugal distortion constants. For the 14N/14N trimer these are (in MHz) for A‘, B‘, and C‘: 2013.5993(10), 1759.2756(3), 932.3709(2); and for τ1, τ2, τaaaa, τbbbb, and τcccc: −0.3017(1), −0.0660(1), −0.1700(9), −0.013 71(1), and −0.0088(1). The inertial defect is 3.7881 amu A2. The zero‐point vibrationally averaged geometry is planar and T shaped with the structure of the linear HCN dimer remarkably unperturbed by presence of the Ar ...

Rovibrational state mixing in the aldehyde C–H stretch fundamental region of acetaldehyde

Abstract: We have studied rovibrational state mixing in acetaldehyde using infrared laser induced fluorescence. Molecules are isolated and cooled in supersonic molecular beams, and irradiated in the C–H stretch fundamental region with an infrared optical parametric oscillator. Spectral resolution is provided with either a circular variable filter machine or a cryogenic Michelson interferometer. We have found evidence of several strong Fermi resonances between the aldehyde C–H stretch and a few overtones and combinations of lower frequency modes. In addition, there is substantial random state mixing in this region as evidenced by the average experimental dilution factor of 0.2. The dependence of the dilution factor on the average J excited by the laser shows that the extent of state mixing scales linearly with J. We have observed from dispersed fluorescence spectra that random rotational coupling occurs between different Kp states. Our previous statistical coupling model has been applied to the interpretation of the...