Laboratory measurements of gas‐phase reactions of polyatomic carbon ions C+n(n=1–6) and CnH+(n=2–5) with carbon monoxide

Even-odd product variation of the C(n)(+) + D(2) (n = 4-9) reaction: complexity of the linear carbon cation electronic states

We have studied reactions between linear Cn(+) (n = 4-9) and D2, using ion mobility mass spectrometry techniques and quantum chemical calculations in order to understand the complex reactivity of the linear cluster cations. Only linear CnD(+) products were observed for the odd (n = 5, 7, 9) linear clusters, while CnD2(+) was the main product for the even clusters. For the reaction rate constants determined for these two channels, we obtained the following two features: (1) the rate constant decreases with the size n, and (2) even-sized clusters have lower rate constants than neighboring odd-sized clusters. In the theoretical calculations using the CCSD(T) and B3LYP methods with the cc-pVTZ basis, we found that a low lying (2)Σ state in odd clusters may play an important role in these reactions. This opposes the previous interpretation that the (2)Πg/u state is the dominant electronic state for linear Cn(+) (n = 4-9) clusters. We showed that a barrierless radical abstraction forming CnD(+) occurs through a direct head on approach for the (2)Σ state Cn(+). In contrast, a carbene-like insertion forming CnD2(+) occurs through a sideways approach for the (2)Πg/u state Cn(+). We have concluded that the higher rate constants for the odd clusters come from the existence of symmetry broken (2)Σ states which are absent in even linear clusters.

Untangling the chemical dynamics of the reaction of boron atoms, 11B(2Pj), with diacetylene, C4H2(X1Σg+)--a crossed molecular beams and ab initio study

A crossed molecular beams experiment with ground state boron atoms, B((2)P(j)), and diacetylene, C(4)H(2)(X(1)Σ(g)(+)), was conducted at a collision energy of 21.1 ± 0.3 kJ mol(-1) under single collision conditions and combined with electronic structure calculations on the (11)BC(4)H(2) potential energy surface. Our combined experimental and computational studies indicate that the reaction proceeds without entrance barrier and involves indirect scattering dynamics. Three initial collision complexes, in which the boron atom adds to one or two carbon atoms, were characterized computationally. These intermediates rearranged via hydrogen shifts and/or successive ring-opening/ring closure processes on the doublet surface ultimately yielding a cyclic, C(s) symmetric (11)BC(4)H(2) intermediate. The latter was found to decompose via atomic hydrogen loss to yield a cyclic (11)BC(4)H(X(1)A') isomer; to a minor amount, the cyclic intermediate isomerized via ring-opening to the linear HCCBCCH(X(2)Σ(g)(+)) molecule, which in turn emitted a hydrogen atom to yield the linear HCCBCC(X(1)Σ(+)) molecule. The overall reactions to form these isomers were found to be exoergic by 55 and 61 J mol(-1), respectively, and involved rather loose exit transition states. On the basis of the energetics, upper limits of two energetically less stable species, the linear HBCCCC(X(1)Σ(+)) and BCCCCH(X(1)Σ(+)) species, were derived to be 12 and 2.2%, respectively. The dynamics of this reaction are also compared with the reaction of ground state boron atoms with acetylene studied earlier in our group.

3Σ-−X 3Σ- Electronic Transition of Linear C6H+ and C8H+ in Neon Matrixes

The electronic absorption spectra of linear C6H+ and C8H+ were recorded in 6 K neon matrixes following mass selective deposition. The (1) 3Sigma- -X 3Sigma- electronic transition is identified with the origin band at 515.8 and 628.4 nm for l-C6H+ and l-C8H+, respectively. One strong (near 267 nm) and several weaker electronic transitions of l-C8H+ have also been observed in the UV. The results of ab initio calculations carried out for linear and cyclic C6H+ are consistent with the assignment.

A priori predictions of the rotational constants for HC13N, HC15N, C5O

Ab initio molecular orbital theory is used to estimate the rotational constant for several carbon-chain molecules that are candidates for discovery in interstellar space. These estimated rotational constants can be used in laboratory or astronomical searches for the molecules. The rotational constant for HC13N is estimated to be 0.1073 +/- 0.0002 GHz and its dipole moment 5.4 D. The rotational constant for HC15N is estimated to be 0.0724 GHz, with a somewhat larger uncertainty. The rotational constant of C5O is estimated to be 1.360 +/- 2% GHz and its dipole moment 4.4. D.