Edward K. C. Lee

ISOTOPIC MOLECULES: SEPARATION BY RECYCLE GAS CHROMATOGRAPHY.

Gas chromatographic columns, greatly extended in length by the use of paired columns in a recycling apparatus, have been used to separate butane (n-C4H10) from deuterated butane (n-C4D10) and methane (CH4) from deuterated methane (CD4). The separation of monotritiated cyclobutane (C4H7T) from cyclobutane (C4H8) is nearly complete. This procedure is generally applicable to a wide variety of separations of isotopic molucules.

Rotational dependence of the fluorescence quantum yields of H2CO and D2CO (? 1A2): single rovibronic level values and their average values for the 41 level

The fluorescence quantum yields, ΦF(K′, J′), of single rovibronic levels (SRVL’s) of the 41 (i.e., ν4′=1) vibrational state of H2CO and D2CO (? 1A2) have been measured at low pressures by laser‐induced fluorescence using a multiple path cell. From these data, the ’’absorption intensity weighted’’ averages of ΦF are obtained for several K′ rotational manifolds as <ΦF(K′) 〉 and for the 41 level as 〈ΦF〉. The latter value of 0.031 confirms the validity of the SVL value of 0.0344 obtained from broad‐band optical excitation by Miller and Lee. A random variation of ΦF (K′, J′) with J′ is observed, and its implication to the question of radiationless transitions in formaldehyde molecules is discussed.

Singlet–singlet electronic energy transfer: Dipole–dipole and exchange contributions

Singlet–singlet electronic energy transfer rates from p‐difluorobenzene to acetone and its methyl‐substituted derivatives have been measured in the gas phase. The results are compared to the data previously obtained with benzene as the donor, within the theoretical framework of the long range Coulombic and the short range exchange mechanisms. It is shown that the small energy transfer rates obtained with the highly substituted ketones can be attributed to the steric hindrance effect associated with the exchange mechanism; the steric hindrance factor in di‐t‐butyl ketone is ∼0.1 compared to acetone. No steric hindrance effect is observed for the dipole–dipole mechanism, as expected.

Pressure dependence of fluorescence quantum yields and collision‐induced rotational relaxation of single rotational levels of H2CO(Ã 1A2, 41)

Pressure dependent values of SRL fluorescence quantum yields Φf(J′, K′) in the 1–120 mTorr range are reported for 75 rotational levels (E′rot = 37–1127 cm−1) of S1 H2CO (41). High lying rotational levels tend to show an increase in Φf with increasing pressure of S0 H2CO, whereas low lying rotational levels tend to show a decrease. For some levels, collision‐induced ΔJ′ transitions occur 5–10 times faster than the gas kinetic collision rate but probably with a much slower rate for ΔK′ transitions. A ΔK′‐constrained, collision‐induced rotational relaxation model involving mainly ΔJ′ = ±1 transitions is proposed to explain the observed pressure dependence of Φf(J′, K′).

On the bonding and structure in dihydroperoxyl (HO2)2 and H2O4

Ultraviolet photolysis of H2CO and C2H2O2 in an O2 matrix at 12–20 K gives (HO2)2. The infrared absorption spectrum of (HO2)2 shows internal hydrogen bonding. A head‐to‐tail, six‐membered cyclic dimer structure is proposed. On warming to 30 K, (HO2)2 disappears and H2O2 is formed.

Rotation‐induced vibrational mixing in S1 H2CO near E′vib =2000–2300 cm−1: 2143 and 214161 levels

Coriolis‐induced vibrational mixing in S1 H2CO near Evib =2000–2300 cm−1 is manifested by the rotational quantum number (J′,K′a) dependent variation of the emission intensity in the rotationally resolved, dispersed fluorescence spectrum. The c‐axis Coriolis resonance between 2143 (Ka=5) and 214161 (K′a=4) is observed with ξ(c)st ≂0.2 cm−1. The b‐axis Coriolis interaction between 214161 (Ka=5) and 4461 (K′a=4) in S1 as well as the a‐axis Coriolis interaction between 42 and 4161 in S0 are observed. A significant degree of vibrational mixing is observed in the energy range, Evib =2000–2300 cm−1.