Christopher J. Whitham

Microwave spectroscopic detection of transition metal hydroxides: CuOH and AgOH

Pure rotational spectra of transition metal hydroxides have been reported. Millimeter wave spectra of CuOH and AgOH were recorded in a direct current discharge absorption cell in the range of 200–390 GHz. The spectra of both molecules correspond to that of a near prolate asymmetric top and only a-type R branch transitions were observed. The rotational and centrifugal distortion constants of CuOH and AgOH were precisely determined. Centrifugal distortion terms up to N2Nz10 were required to fit the observed line frequencies of 63CuOH. A preliminary analysis showed that AgOH is also strongly bent like CuOH with a bond angle smaller by about 2°.

The vibrational state distributions in both products of the reaction: O(3P) + NO2 → O2 + NO

Abstract A laser pulse-and-probe method has been used to determine the nascent vibrational populations in NO( v =0–4) and O 2 ( v =6–11) formed in the thermal reaction: O( 3 P) + NO 2 → O 2 ( v ) + NO( v ). A frequency-tripled Nd: YAG laser is used to photolyse NO 2 , diluted tenfold in Ar, and laser-induced fluorescence spectroscopy in the NO A 2 Σ + -X 2 Π and O 2 B 3 Σ − u -X 3 Σ − g electronic band system is used both to follow the kinetics of individual vibrational states and to determine the nascent vibrational distributions. The majority of the NO product is formed in v = 0 and the average vibrational yield is ≈ 4.6%. The O 2 populations fall monotonically from v = 6 to 11 in a distribution close to what is expected on prior grounds. Based on a surprisal analysis, the average vibrational energy yield in O 2 is ≈ 26%. The nature of the reaction dynamics is discussed.

Microwave spectra of CuOD and AgOD: Molecular structure and harmonic force field of CuOH and AgOH

Pure rotational spectra are reported for the deuterated species of copper and silver hydroxide, 63CuOD, 107AgOD, and 109AgOD. Together with the CuOH and AgOH data previously reported, a number of harmonic force constants were determined. These constants are interpreted in terms of the balance between competing ionic and covalent interactions. The harmonic force field allowed the rz structures to be determined. Both molecules are strongly bent indicating considerable covalent character.

The production of vibrationally excited NCO(X̃ 2Π) in the reaction between CN radicals and O2

Abstract Experiments of two kinds have been performed to determine the vibronic state distribution in NCO(X 2Π) produced in the radical—radical reaction CN+O2→NCO+O; ΔH00=−29±6 kJ mol−1. In both experiments, CN radicals are produced by photolysis of NCNO using a frequency-doubled Nd:YAG laser. NCO radicals are observed as products of the reaction with O2, either by recording laser excitation spectra at short times after the initiation of reaction, or by fixing the probe laser frequency and recording the variation of laser-induced fluorescence with the time delay between photolysis and probe lasers. NCO is produced in a wide range of vibronic levels. Insufficient information about band intensities is available to transform the spectra into relative populations. However, the ν2 bending vibration is highly excited and this mode absorbs ∼ 50–60% of the energy available to the products. The stretching modes absorb ≈ 15–20% of the energy. The implications of these results for the dynamics of reactive collisions between CN and O2 are discussed.

Vibrational state specificity and selectivity in the reactions N+OH→NO(v)+H and N+NO(v)→N2+O

The vibrational state distribution of NO formed in the radical–radical reaction N+OH→NO(v’≤9)+H; ΔH00=−204.0 kJ mol−1 has been determined using a pulse‐and‐probe technique. OH radicals were generated by pulsed laser photolysis of H2O2 at 266 nm in a flow of N2 which had been passed through a microwave discharge to produce N atoms. The vibrational distribution of NO, measured by laser‐induced fluorescence (LIF) spectroscopy, is similar to that predicted by phase‐space theory and corresponds to an average yield of ca. 31% of the energy available to the reaction products. Experiments in which LIF signals were observed as the pulse–probe time delay was varied showed that populations within different vibrational levels (v=0–8) displayed similar kinetics, consistent with rapid removal of NO(v) by reaction with N atoms, N+NO(v)→N2+O, at rates which exhibit a mild dependence on v.

Rotational spectra of the H2-HCN cluster observed by millimeter-wave spectroscopy combined with a pulsed supersonic jet technique

Millimeter-wave spectroscopy combined with a pulsed supersonic jet technique was used to observe rotational lines of the H2–HCN cluster containing the ortho as well as para hydrogen molecule. The Σ symmetry in the ground state was confirmed for both species. From the observed rotational constants, the average distance between the center of mass of H2 and that of HCN was derived to be 3.9613 (35) A for the ortho species and 4.229 (11) A for the para species. The results suggest totally different configurations in the ortho and para species: H2 is attached to the hydrogen end of HCN in the para species, while to the nitrogen end in the ortho species. The nuclear quadrupole interaction constants show that the HCN part executes a floppy motion with a large mean amplitude of about 30° in the ortho, as well as para, species.

Evidence for Renner-Teller coupling in the upper, triplet electronic state of the 370 nm system of InOH

Abstract The gross features of the recently observed ultraviolet band system of InOH are explained in terms of transitions from the ground 1 A′ to components of an excited triplet state in which the molecule is also bent. The triplet state correlates with a 3 Π state in the linear configuration and is subject to a large Renner-Teller effect.