W. H. Green

Measurement of CO(ν = 1) vibrational energy transfer rates using a frequency‐doubled CO2 laser

Laser‐induced fluorescence studies of CO collisional relaxation have been carried out using the output of a frequency‐doubled, pulsed CO2 laser as a direct source of CO(ν = 1) excitation. Energy transfer cross sections at 298 °K are reported for CO in collisions with He, Ar, H2, D2, N2, O2, Cl2, NO, CH4, CF4, and SF6. The D2–D2 self‐relaxation rate was also obtained from the analysis of CO–D2 mixtures.

Vibrational Deactivation of HF(v=1) in Pure HF and in HF‐Additive Mixtures

The laser‐excited vibrational fluorescence method has been used to obtain room temperature (294±2°K) vibrational relaxation rates for pure HF and in HF‐additive mixtures. Measurement of the quenching of HF(v=1) fluorescence in HF–HF and HF‐additive collisions has yielded the following total deactivation rates: HF†Ar<60 sec−1· torr−1, HF†N2=(1.25 ± 0.6) × 102  sec−1· torr−1, HF†D2=(3.7± 0.4)× 103sec−1· torr−1, HF†H2=(2.4 ± 0.3) × 104sec−1· torr−1, HF†CO2=(5.9± 0.2)× 104 sec−1· torr−1, and HF†H2O≈ HF†D2O=(4.1± 0.5)× 106  sec−1· torr−1. The self‐relaxation rate for HF was found to be HF†HF=(8.74± 0.1)× 104  sec−1 torr−1 in dilute Ar mixtures and also with other additives. A slower rate (4.4± 0.3)× 104 sec−1· torr−1 has been measured in pure HF and is believed to indicate nonequilibrium of the rotational degrees of freedom during self‐relaxation of HF. Observation of 4.3 μ fluorescence from CO2(00°1) and double exponential fluorescent decay from HF–H2 mixtures has led to the following rates for CO2(00°1) and ...

Spectra and Structure of Small Ring Compounds. XX. Fluorocyclobutane

The infrared spectrum of fluorocyclobutane vapor has been recorded from 4000–33 cm−1. The infrared spectrum of the solid at − 196°C has been recorded from 4000–200 cm−1. The Raman spectra of the liquid at room temperature and the solid have been recorded and depolarization values have been measured. The spectra have been interpreted on the basis of a puckered model ring with only one conformation which has a plane of symmetry and belongs to the Cs point group. Assignment of the 30 normal vibrations has been based on depolarization values, band contours, group‐frequency correlations, and relative intensities. A series of four Q branches was observed in the far‐infrared spectrum and has been interpreted as arising from the fundamental and “upper‐state” transitions of the anharmonic ring‐puckering vibration. The series could be fit equally well by two different double‐minima potential functions, one with a relatively high barrier of 803 cm−1 and the other with a 485‐cm−1 barrier. On the basis of previous mic...

Vibrational deactivation of carbon monoxide by hydrogen and nitrogen from 100 to 650 °K

Collisional quenching of carbon monoxide by hydrogen and nitrogen has been studied in the 100–650°K temperature range using the laser excited vibrational fluorescence method. The rate constant for CO–H2 deactivation increases smoothly with temperature from 2.6±0.3 sec−1·Torr−1 at 112°K to 170±15 sec−1·Torr−1 at 623°K. The vibration‐to‐vibration energy transfer results for CO–N2 mixtures (exothermic direction) show only a slight temperature dependence from 103 to 651°K with a broad maximum of 420±30 sec−1·Torr−1 in the temperature range 300–400°K. Comparison of our rates with high temperature shock tubes results show excellent agreement for the CO–H2 V → R,T process and only fair agreement for the CO–N2 V → V exchange process. This latter discrepancy may be partially due to the uncertainties involved in extracting V → V energy transfer rates from shock tube data.

Measurement of the rate of excitation and deactivation of OCS(001), N2O(001), CS2(001), and C2N2(00100) using laser excited CO as a pumping source

The laser fluorescence method has been used to measure CO(ν=1) collisional transfer rates in several binary and ternary gas mixtures at 296°K. Excitation of the CO(ν=1) level was achieved using pulsed 4.6 μm radiation from a frequency doubled CO2 laser. The relative inertness of CO molecules towards V→T deactivation greatly facilitates the study of vibrational relaxation rates of the additive species in selected cases. In this paper, intermolecular V→V transfer rates at 296°K are reported for CO(ν=1) with N2O, OCS, SO2, CS2, C2N2, and for CO(ν=2) with CO. In addition, the additive deactivation rates were determined for the following collisional processes: N2O(001) with N2O, CO, Ar; OCS(001) with OCS, CO, Ar; CS2(001) with CS2, CO; and C2N2(00100) with C2N2 and CO.

Ring‐Puckering Vibration of 2,3‐Dihydrofuran

The far‐infrared spectrum of 2,3‐dihydrofuran vapor has been examined from 33 to 500 cm−1. Twelve sharp Q branches have been observed between 70 and 350 cm−1. These bands are assigned to transitions of the anharmonic ring‐puckering vibration which is described by the following relation in reduced coordinates: V(cm−1) = 28.3(x4 − 3.44 x2). Such a potential predicts a puckered molecule in the ground and first excited states, a barrier to planarity of 83 cm−1, and a 0–1 transition of 20.5 cm−1. There is considerable disagreement between the previously predicted far‐infrared spectrum and that observed.

Vibrational Spectra and Structure of Dimethyl Diselenide and Dimethyl Diselenide‐d6

The vibrational behavior of the dimethyl diselenide and dimethyl diselenide‐d6 molecules has been studied in the infrared region (4000–70 cm−1) and by Raman shifts (4000–50 cm−1). The molecule has been found to belong to point group C2. The fundamental vibrations, with the exception of the methyl torsions, have been assigned and supported by a normal‐coordinate analysis.

Ring‐Puckering Vibration of 2,5‐Dihydrothiophene

The infrared spectrum of 2,5‐dihydrothiophene has been measured from 80 to 4000 cm−1. The far‐infrared region contained sharp Q branches at 87.0, 95.5, 102.0, 107.0, 111.2, 114.8, 118.1, 120.7, 123.2, 125.2, and 127.0 cm−1 which have been assigned to single quantum transitions between the first 12 levels of the ring‐puckering vibration. A mixed harmonic–quartic potential‐energy function has been fitted to the observed frequencies and is described by the following relation in reduced coordinates: V(cm−1) = 16.86 (x4 + 5.93x2). Such a potential function can be rationalized only in terms of a planar ring skeleton with no barrier to inversion. Two combination and one difference band series of the ring‐puckering transitions with fundamentals centered near 3064, 670, and 2865 cm−1, respectively, have also been studied. The ring‐puckering transitions obtained from the 670‐cm−1 band series agree favorably with the far‐infrared frequencies; however, those in reference to the two carbon–hydrogen stretching fundamen...

Spectroscopic Determination of the Pseudorotation Barrier in Selenacyclopentane

The infrared and Raman spectra of selenacyclopentane have been studied. A series of far‐infrared absorption peaks is interpreted to indicate that the five‐membered ring molecule has a large barrier to pseudorotation. The derived potential function is V(φ) in cm−1 = − (1795.4 / 2)[1 − cos(2φ)] + (13.45 / 2) × [1 − cos(4φ)] − (86.19 / 2)[1 − cos(6φ)] with the pseudorotation constant B = 1.55 cm−1. Evidence that the molecule has a twisted (c2) configuration in its lowest few vibrational states has been obtained.

Vibrational deactivation rates of HF(ν = 1) by CH4, C2H6, C3H8, C4H10, C3H6, and ClF3

The rates at which vibrationally excited HF is deactivated by CH4, C2H6, C3H8, C4H10, C3H6, and ClF3 have been measured to be (5.3 ± 0.8) × 104; (1.10 ± 0.16) × 105; (1.35 ± 0.2) × 105; (1.7 ± 0.25) × 105; (3.2 ± 0.5) × 105 and (1.13 ± 0.17) × 105 sec−1 · torr−1, respectively, using the laser‐excited vibrational fluorescence technique. It was found that the cross‐section for HF deactivation by the lower alkanes, Cn H2n+2, varied linearly with n. The deactivation rate measured for HF–ClF3 is orders of magnitude greater than has been observed for HF deactivation by other fluorine sources. The importance of the above rate measurements in the understanding and analysis of pulsed HF lasers is discussed in detail.