Chemiluminescence in the Reaction of Mn Atoms with SiCl₄

Abstract

Chemiluminescence in four different MnCl band systems  e5Σ+ → a5Σ+ (“blue”), d5Π → a5Σ+ (“green”), c5Σ+ → a5Σ+ (“red”), and b5Π → a5Σ+ (“infrared”)  has been observed from the interaction of a laser-ablated beam of Mn atoms with gaseous SiCl4. The initial translational thresholds range from ∼150 to ∼300 kJ mol-1, increasing in the order e5Σ+ < c5Σ+ ∼ d5Π < b5Π. Analysis of the measured excitation functions, in terms of a multiple line-of-centers model [Levy, M. R. Res. Chem. Kinetics 1993, 1, 163], shows that, with the exception of a high-energy c5Σ+ channel contribution to d5Π production and possibly a joint c5Σ+/d5Π production process at low energies, all the reactions take place on distinct potential surfaces. Although, on energetic grounds, the b5Π and c5Σ+ channels could derive from reaction of ground-state Mn(a6S) atoms, the first excited state, a6DJ, is the most likely reagent species in all cases, indicating substantial excess barriers. In contrast to the corresponding SnCl4 reactions, only the c5Σ+ excitation function reveals a shift forward in transition-state location with increasing collision energy. The results have been rationalized in terms of a hierarchy of ionic−covalent curve crossings at short internuclear distances.

Chemiluminescence in the Reaction of Mn Atoms with CF4

“…Indeed, with its low depletion threshold and high depletion probability, this initial feature is more akin to those Mn-halide excitation functions that show a transition state shift than to those that do not. [9][10][11] The threshold at ∼670 kJ mol -1 suggests the opening up of a new reaction channel, perhaps involving a different reagent state, as does the threshold at ∼1811 kJ mol -1 . However, as pointed out earlier, the σ 3 term could be an artifact due to the rising edge of the beam pulse.…”

“…As pointed out in the Introduction, chemiluminescence in Mn + SnCl 4 , SiCl 4 , SF 6 has been rationalized 9,11,12 in terms of an ionic-covalent curve crossing model in which the emitting states derive only from excited ionic potentials. The crossings with these curves are estimated to occur at very short internuclear distances, which can only be achieved if the Mn approaches the central atom (Sn, Si, S) along or close to a C 3 axis.…”

“…We have rationalized such "simple fall-off" in terms of competition between (a) reaction, with probability P 0 at internuclear distance R 0 and line-of-centers will clearly show an initial linear rise, then a reduced slopesperhaps even zero slopesfrom E 1 . Comparison of the slopes of the two linear regions yields from which a lower limit to either P d or R d /R 0 is obtained, [9][10][11]13 since P d e 1.0 and R d is not expected to be substantially larger than R 0 .…”

Cluster isolated chemical reactions: Reactivity of Ba atoms and small Ba clusters with SF6 and CO2 molecules on large argon clusters

“…34 The observations of chemiluminescent channels in MnϩSF 6 reactions have been rationalized on the basis of an energy barrier that prevents the formation of the reactive intermediate Mn ϩ SF 6 Ϫ .…”

State-to-state chemiluminescence in reactions of Mn atoms with S2Cl2

“…Work from this laboratory has concentrated on reactions of Mn, partly due to relative ease of study, but also because the first metastable state, a 6 D J , is situated more than 2 eV above the a 6 S ground state, 16 allowing the reactivity of the two to be more readily separated and assigned. In studies of Mn + halogens and halides, 10,[17][18][19][20][21][22] translational excitation functions s(E T ) for chemiluminescence in the MnF and MnCl A 7 P-X 7 S + , e 5 S + -a 5 S + , d 5 P-a 5 S + , c 5 S + -a 5 S + and b 5 P-a 5 S + band systems have been measured. Analysis of the data in terms of the multiple-line-of centres (MLC) expression [10][11][12][17][18][19][20][21]23 Y(E T ) = E T s(E T ) = P s k (E T À E k ),…”