A B S T R A C TWe have calculated synthetic spectra of perpendicular and parallel rovibronic bands of cumulene carbene molecules of the form C n H 2 . The perpendicular bands are consistent with a regularly spaced group of diffuse interstellar bands (DIBs) near 6850 A Ê . Parallel bands calculated for these molecular structures are consistent with the intrinsic profile of the associated 6614-A Ê DIB. Both types of bands are expected for an electronic transition that these species should have at those energies. We could not determine if the molecule was charged or if an atom other than carbon terminated the chain-end. Constraints due to molecular geometry and temperature place the chain length at 7±15 carbons to fit the 6850-A Ê group and 9±13 carbons to fit the 6614-A Ê DIB.
The first known experimental studies of two-center three-electron bonding involving tellurium in the gas, liquid, or solid state are reported. Ions studied include: [(CH 3 ) 2 Te∴Te(CH 3 ) 2 ] + , [(CH 3 ) 2 Te∴Se(CH 3 ) 2 ] + , [(CH 3 ) 2 Te∴S(CH 3 ) 2 ] + , and [(CH 3 ) 2 Te∴ICH 3 ] + . Metastable and collision-induced dissociation tandem mass spectrometry methods were employed to investigate the structures of the ions. The metastable spectra show direct cleavage of the Te∴Te, Te∴Se, Te∴S, and Te∴I bonds yielding product ions with the charge on the Te containing moiety (that with the lowest ionization energy). Collision-induced dissociation spectra show intense peaks for these same fragments. The collision-induced dissociation spectra also show peaks for almost every possible methyl loss, suggesting large collision-induced dissociation cross sections for the methyl losses and/or weak Te-CH 3 , Se-CH 3 , S-CH 3 , and I-CH 3 bonds. These spectra are consistent with Te∴Te, Te∴Se, Te∴S, and Te∴I hypervalent interactions. Equilibrium experiments on (CH 3 ) 2 Te •+ + Te(CH 3 ) 2 + M a [(CH 3 ) 2 Te∴Te(CH 3 ) 2 ] + + M resulted in ∆H rxn °) -97 ( 2 kJ/mol and ∆S rxn °) -81 ( 3 J/(K‚mol). Since in this specific reaction, ∆H rxn °) -∆H bond °, the experiment yields a bond enthalpy of 97 ( 2 kJ/mol at 516 K. We believe that these are the first experiments on 2c-3e bonding involving tellurium and thus this article includes the first known experimental Te∴Te bond enthalpy.
We report an experimental study of the metastable and collision-induced dissociation spectra of association
adducts with the suggested general formula [c-C
n
H2
n
S∴ICH3]+ where n = 2, 3, 4, and 5. These association
adducts are examples of gas-phase cations which may contain 2c−3e sulfur−iodine bonding interactions.
Metastable cleavage of the sulfur−iodine bonds result in predominately one reaction, [c-C
n
H2
n
S∴ICH3]+ →
c-C
n
H2
n
S•+ + CH3I; this reaction cleaves the proposed 2c−3e bond. The product ion for each adduct exhibits
a small average kinetic energy release implying a fragmentation with a small or no reverse activation barrier.
Fragmentation by collision-induced dissociation yields two intense product peaks and numerous weaker peaks.
These metastable and collision-induced dissociation results support hypervalent S∴I bonding within the ionic
adducts. The spectra also suggest that the sulfur-containing moieties in the adducts are ring-closed.
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