Rotational Alignment in MnO*(A⁶Σ⁺) from the Reaction Mn + O₂

Abstract

The collision energy dependence of chemiluminescence, and its polarization relative to the initial velocity vector k, has been determined for MnO*(A 6 Σ + ) product from the Mn + O 2 reaction in the range 0-1500 kJ mol -1 . Analysis of the excitation function by the multiple line-of-centers approach indicates that three parallel processes, attributed to a 4 D J , z 8 P J (perhaps), and a 6 D J atoms, contribute. All seem to involve a significant excess barrier and a forward transition state shift with increasing collision energy, suggesting that reaction proceeds via inner ionic-covalent curve crossings at short internuclear distances. The measured alignments are relatively modest, indicating a predominant contribution to MnO rotation from O-O recoil in a nonlinear Mn-O-O configuration.

Chemiluminescence from the Ba(P3)+N2O→BaO(A Σ1+)+N2 reaction: Collision energy effects on the product rotational alignment and energy release

“…In the present experimental configuration, ͗P 2 ͑k · z͒͘ depends on the masses of the beam and gas species, the temperature of the latter and the nominal collision energy ͑E c 0 = ͑1 / 2͒͑x / t͒ 2 ͒ through one reduced parameter. 38 As shown previously, 8 it is reasonable to assume that ͗P 2 ͑k · z͒͘ ϳ 1 for the reactive collision energies employed in the present experiments. Figure 3͑c͒ displays the conversion of the P͑͒ data presented in Fig.…”

Chemiluminescence and rotational alignment in Mn+O2: Direct observation of the MnO*(A′ 6Π) state

“…However, as in ref. 7, this is discounted since the polarisation measurements (Fig. 4) indicate the onset of a new reaction channel at E T 0 D kJ mol~1.…”

Chemiluminescence and rotational alignment in Mn*(a 4DJ, a 6DJ)+SO2→MnO*(A′ 6Π, A 6Σ+)+SO

“…For chemiluminescence alignment, however, such an arrangement raises problems of both di †erential sensitivity drift with time and subtle di †erences in the wavelength dependence of the beamsplitter s-plane and p-plane transmissions. 7 We therefore employ the vertically-mounted photomultiplier, which detects emission " straight-through Ï the cube, to make sequential measurements of the emission intensity perpendicular and I M v , I A v parallel to the Mn beam axis, while the horizontal photomultiplier (" reÑected Ï emission) acts as a contemporaneous reference in recording only the parallel-polarised signal After I A h . averaging, these data are converted to ratios and…”

“…Furthermore, if v@ continues to increase, then the peak A 6&`] X 6&`emission may pass beyond the range of the Ðlter combination, i.e. for the (6,10) and (7,11) transitions occurring at 703 and 707 nm respectively. 34 Clearly, similar considerations must apply to the IR band system, about which so little is known.…”

“…For the higher-threshold A 6&`processes at least, the MnO* rotational alignment is initially high but falls rapidly with increasing energy, consistent with line-of-normals behaviour in which k lies within the MnÈOÈO plane at threshold but departs increasingly from it as collision energy increases. 7 In the analogous A@ 6% case, however, appears [SP 2 ( j ü @ AE k ü )T Ðrst to rise, then fall. Given the common thresholds, this has been interpreted in terms of a common reactive process in which either near-linear or collisions give rise to C 2v MnO*(A@ 6%) product, and less restricted geometries to MnO*(A 6&`).…”