Theoretical investigation of the infrared spectrum of small polyynes

Abstract

aThe full cubic and semidiagonal quartic force fields of acetylene (C 2 H 2 ), diacetylene (C 4 H 2 ), triacetylene (C 6 H 2 ), and tetraacetylene (C 8 H 2 ) are determined using CCSD(T) (coupled cluster theory with single and double excitations and augmented by a perturbative treatment of triple excitations) in combination with the atomic natural orbital (ANO) basis sets. Application of second-order vibrational perturbation theory (VPT2) results in vibrational frequencies that agree well with the known fundamental and combination band experimental frequencies of acetylene, diacetylene, and triacetylene (average discrepancies are less than 10 cm À1). Furthermore, the predicted ground state rotational constants (B 0 ) and vibration-rotation interaction constants (a i ) are shown to be consistent with known experimental values. New vibrational frequencies and rotational parameters from the presented theoretical predictions are given for triacetylene and tetraacetylene, which can be used to aid laboratory and astronomical spectroscopic searches for characteristic transitions of these molecules.

Alternation of Singlet and Triplet States in Carbon‐Based Chain Molecules and Its Astrochemical Implications: Results of an Extensive Theoretical Study

“…Unfortunately, ab initio (e.g., CC‐)methods to compute vibrational properties for such large and open shell molecular species, which can be employed to smaller closed‐shell chains, are currently prohibitive. Still, we believe that that the significant differences between Figure a,b (and between Figure S12a,b, Supporting Information) represent a convincing argument that experiments—which the present theoretical study hopes to motivate—can discriminate between the singlet and triplet HC 11 H (and HC 12 H) chains.…”

“…One should mention in this context that zero‐point energy corrections within ab initio approaches like CCSD and CCSD(T) are very challenging; they require costly numerical frequency calculations. Currently, feasible studies of this kind are restricted to closed ‐shell (i.e., singlet but not triplet) species and smaller molecular sizes . As a trade‐off between accuracy and computationally demanding ab initio frequency calculations, zero‐point energy corrections can be applied within the DFT/B3LYP approach.…”

Theoretical Studies of Two Key Low-Lying Carbenes of C5H2Missing in the Laboratory

“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24] Of note, for the confirmation of four C n H 2 carbenes in non-terrestrial environments, [1][2][3][4] identification of the same in laboratories (terrestrial environments) is a crucial factor. 1,11,[25][26][27] Therefore, considering the astrochemical relevance, available laboratory astrophysics data, and enhancing our understanding of structure and bonding of various C n H 2 isomers, where, n = 2, 28 3, 1,2,24,25,29-33 4, 3,27,[34][35][36] 5, 11-24 6, 4,11,34-37 7, 12,24,38-49 8, 34,35,39,50 9, 12,24,38,39,41,43,[51][52][53] etc., in this work, the electronic structures and spectroscopic properties of two additional singlet low-lying C 5 H 2 isomers, buta-1,3-diynylcarbene (6) and 9, have been investigated in detail. Both 6 and 9, in addition to bent-pentadiynylidene (4), 54 are yet to be identified in the laboratory.…”

Reactivity of Polyynes: Complex Molecules from Simple Carbon Rods

“…[60] As a result variety of hexasubstituted benzenes (21)(22)(23)(24)(25)(26)(27)(28) were obtained. The use of terminal triyne caused formation of product with terminal triple bond reacted (28). If hexatriyne with one less bulky methyl group was used a mixture of two possible isomers 26 and 27 was obtained.…”

“…Polyynes also possess a remarkable application potential as molecular wires and switches in nanoelectronics, [7][8][9][10][11] as materials for optoelectronics due to their nonlinear optical response, [12][13][14][15][16][17][18] as precursors of conducting polymers [19,20] or even in live-cells imaging and sorting. [26] Moreover, such molecules have been objects of robust calculations related to astrochemistry [27][28][29] as well as the theoretical attempts to prediction of properties of the elusive carbyne. [26] Moreover, such molecules have been objects of robust calculations related to astrochemistry [27][28][29] as well as the theoretical attempts to prediction of properties of the elusive carbyne.…”