Michel Grutter

Electronic absorption spectra of linear C6, C8 and cyclic C10, C12 in neon matrices

The electronic absorption spectra of the even-numbered carbon molecules C6–C14 have been measured in neon matrices. Bare carbon anions were produced in a cesium sputter source, mass selected, codeposited with neon at 6 K, and neutralized. The spectra show, apart from the known (1) 3Σu−←X 3Σg− transition of linear C6, C8, and C10 in the visible, absorption bands in the UV region. The spectral data when considered in conjunction with ab initio calculations show that the linear forms of C6 and C8 have the next strong (2) 3Σu−←X 3Σg− transition with band maximum near 238 and 277 nm, respectively, whereas the band systems of C10, C12, and C14 at 316, 332, and 347 nm are due to the monocyclic species.

Infrared bands of mass-selected carbon chains Cn (n = 8−12) and Cn− (n = 5−10, 12) in neon matrices

Abstract Infrared bands of carbin chains C n ( n = 8−12) and C − ( n = 5−10, 12) have been observed in neon matrices in the 1600–2100 cm −1 region. The matrices were grown at 5 K by codepositing mass-selected carbon anions with excess of neon. The neutral carbon chains were obtained from the anions by photodetachment. The assignments of the infrared transitions are based on mass-selection, photobleaching behaviour, intensity correlation with the known electronic transitions, and available ab initio calculations.

Electronic absorption spectra of C2nH−,C2n−1N− (n=4–7), and C2n−1N (n=3–7) chains in neon matrices

The 1Σ+←X 1Σ+ electronic transition of the C2nH− and C2n−1N− (n=4–7) anion chains has been observed following mass selection and codeposition with excess neon at 6 K. Photodetachment of the electron resulted in the detection of a band system due to the neutral C2n−1N radical. The spectra suggest that C7N, like C5N, has a 2Σ ground state. The B 2Π←X 2Π transition is detected for the larger C2n−1N (n=5–7) chains. These appear at slightly higher energies than those of the isoelectronic C2nH radicals and show similar spectral features. Several infrared transitions of the anions have also been observed.

Electronic absorption spectra of C4− and C6− chains in neon matrices

The absorption spectra of the electronic transitions A 2Σg+←X 2Πg, B 2Σu+←X 2Πg, (2) 2Πu←X 2Πg, and (3) 2Πu←X 2Πg of C4−, as well as A 2Σg+←X 2Πu, (2) 2Πg←X 2Πu, and (3) 2Πg←X 2Πu of C6− have been obtained in neon matrices. The spectra were measured after mass-selected deposition of the anions with excess of neon at 5 K. The assignments are based on mass-selection, spectroscopic evidence, photobleaching behavior, and ab initio calculations. Vibrational frequencies in the electronically excited states have been inferred.

The 3Σu− ← X3Σg− electronic absorption spectrum of linear C4 in a neon matrix

Abstract The electronic absorption spectrum of linear C 4 in a neon matrix has been detected. This was achieved by codepositing mass selected C 4 − ions with an excess of neon and UV irradiation of the matrix during or after deposition. Mass selection, experimental and spectroscopic evidence, available ab initio calculations and comparison with the spectra of C 2 n ( n =3–7) chains lead to the conclusion that the observed band system with origin at ≈ 380 nm is due to the 3 Σ u − ←X 3 Σ g − transition of linear C 4 . Vibrational frequencies of C 4 in the excited electronic state have been inferred.

Electronic spectra of long odd-number carbon chains C17–C21 and C13−–C21−

Abstract Electronic transitions of the odd-number neutral and anionic carbon chains C 2 n +1 ( n =8–10) and C 2 n +1 − ( n =6–10) have been observed in a neon matrix at 6 K after co-deposition with laser-vaporized graphite. The assignments are based on a comparison with the previously identified electronic transition of C 7 to C 15 and C 5 − to C 11 − , and the monotonic wavelength dependence of the origin band on the number of carbon atoms. The 1 Σ + u ← X 1 Σ + g transition of C 17 to C 21 appears between 455 and 544 nm. The A 2 Π ← X 2 Π transition of C 13 − to C 21 − falls in the 1052–1675 nm region.

Electronic absorption spectra of carbon chain anions C2n− (n=4–7) in neon matrices

Electronic transitions, (2)2Π←X 2Π (n=4–7), 2Σ←X 2Π (n=4,5) in addition to the known one C 2Π←X 2Π (n=4–7) of linear carbon anions C2n− have been observed in neon matrices. Absorption spectra were measured after mass-selected deposition of the anions with excess of neon at 5 K. The assignments are based on mass-selection, wavelength dependence of the 000 transition on size, photobleaching behavior, and ab initio calculations. Vibrational frequencies in the excited electronic states have been inferred. The band system attributed previously to the 3Σu− ←X 3Σg− transition of C10, C12, and C14 is shown to be the (2)2Π←X 2Π transition of their anions. Another set of weak bands is assigned to the 3Σu−←X 3Σg− system of C10 but none were discernible for C12 or C14. This is experimental evidence for the predicted change from linear to nonlinear geometries for the even numbered carbon species larger than C10.

Emission spectrum of mass-selected C4−:C2Πu → X2Πg in a neon matrix

Abstract The laser excited emission spectrum of the C 2 Π u → X 2 Π g electronic transition of mass-selected C 4 − embedded in a 5 K neon matrix has been observed. This is an extension of the technique coupling mass spectrometry and matrix isolation and allows information on the vibrational frequencies of the species in the ground state to be obtained. In the case of C 4 − , three vibrational frequencies ( ν 1 ( σ g + ) = 2047(20), ν 2 ( σ g + ) = 936(20) and ν 4 ( π g ) = 396(20) cm −1 ) have been inferred for the X 2 Π g state.

Diffusion of mass-selected carbon atoms and molecules in argon and neon matrices

Annealing reactions of carbon atoms, molecules, and their anions, trapped in noble gas matrices, were studied spectroscopically. To this aim Cn− (n=1–4) anions were mass-selected and codeposited with argon or neon to form matrices at low temperatures. The charged species were neutralized by uv irradiation. Carbon chain elongation is observed only if neutral or charged atomic carbon is present in the matrix. Spectra of linear carbon clusters up to C11 were observed after C− deposition, electron detachment, and subsequent annealing. The reaction between two Cn (n⩾2) species in solid argon or neon was studied and can be disregarded even at temperatures near the point of matrix sublimation.Annealing reactions of carbon atoms, molecules, and their anions, trapped in noble gas matrices, were studied spectroscopically. To this aim Cn− (n=1–4) anions were mass-selected and codeposited with argon or neon to form matrices at low temperatures. The charged species were neutralized by uv irradiation. Carbon chain elongation is observed only if neutral or charged atomic carbon is present in the matrix. Spectra of linear carbon clusters up to C11 were observed after C− deposition, electron detachment, and subsequent annealing. The reaction between two Cn (n⩾2) species in solid argon or neon was studied and can be disregarded even at temperatures near the point of matrix sublimation.