Electronic structure calculations on the C4 cluster

Abstract

The ground and the electronically excited states of the C 4 radical are studied using interaction configuration methods and large basis sets. Apart from the known isomers ͓l-C 4 ͑X 3 ⌺ g − ͒ and r -C 4 ͑X 1 A g ͔͒, it is found that the ground singlet surface has two other stationary points:form is the third isomer of this cluster. The isomerization pathways from one form to the other show that deep potential wells are separating each minimum. Multireference configuration interaction studies of the electronic excited states reveal a high density of electronic states of these species in the 0 -2 eV energy ranges. The high rovibrational levels of l-C 4 ͑ 3 ⌺ u − ͒ undergo predissociation processes via spin-orbit interactions with the neighboring 5 ⌺ g + state.

A sensitivity study of the neutral-neutral reactions C + C$_{\sf 3}$ and C + C$_{\sf 5}$ in cold dense interstellar clouds

“…The high-temperature experimental value has been used in the RRKM calculations discussed below. The rhombic isomer of C 4 in its ground singlet state has been calculated to to be nearly isoenergetic with the linear isomer (Masso et al 2006), but the pathway from C and linear C 3 to the first excited triplet state shows a high barrier at the CASSCF level of ab initio theory (see below). In the C ∞,v symmetry, the three electronic states of C 4 correlating to the three spin-orbit states of C( 3 P 0,1,2 ) lead to two different potential energy surfaces corresponding to the fundamental state X 3 Σ − g and the first excited 3 Π g state.…”

Raman and infrared spectra of dimethyl ether 13C-isotopologue (CH3O13CH3) from a CCSD(T) potential energy surface

“…where K 3 and K 7 are equivalence classes of g 36 (see Table 1), and K' 2 and K' 4 are equivalence classes of C 2v {M) (see Table 2). The sum of all the symmetry elements belonging to the classes in Eq.…”

“…For Sis, the symmetry of the molecular dipole moment in the laboratory axis system r(fi A ) = A 2 but the infrared transitions, corresponding to the Q. branches of c-type bands are given by the symmetry of the c-component of the molecular dipole moment in the molecular fixed axis system r(fi c ) =A 2 .…”

“…For DME- 13 C, the ZPVE correction V ZPVE has been determined in present paper from the MP2/aug-cc-pVTZ harmonic frequecies co, of the remaining vibrational modes: (2) i=n+l where the sum neglects the two torsional and the COC bending modes (n = 3) and runs over the total number of vibrational modes in the molecule (3 N-6).…”

“…Although many isotopic varieties containing 13 C have been spectroscopically characterized to allow their astronomical detection (i.e. for C 4 [2], C 5 [3], methanol [4], methyl formate [5,6], ethyl methyl ether [7]), the 13 C isotopologues of many other species cannot be identified in the ISM due to the lack of their spectral recordings. This is the case of dimethyl ether (DME).…”