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In the last 30 years, our research has focused on laboratory measurements of the electronic spectra of organic radicals and ions. Many of the species investigated were selected based on their potential astrophysical relevance, particularly in connection with the identification of appealing candidate molecules for the diffuse interstellar absorptions. Notably, carbon chains and derivatives containing hydrogen and nitrogen atoms in their neutral and ionic forms were studied. These data could be obtained after developing appropriate techniques to record spectra at low temperatures relevant to the interstellar medium. The measurement of gas phase laboratory spectra has enabled direct comparisons with astronomical data to be made and though many species were found to have electronic transitions in the visible where the majority of diffuse bands are observed, none of the absorptions matched the prominent interstellar features. In 2015, however, the first carrier molecule was identified: C+60. This was achieved after the measurement of the electronic spectrum of C+60-He at 6K in a radiofrequency ion trap. [ABSTRACT FROM AUTHOR]

Two-photon absorption spectroscopy with a mass-selected beam of CO+2 ions was used to study the predissociative C 2Σ+g state of CO+2. The first photon pumped the A 2Πu←X 2Πg transition and the second photon was used to scan through the C 2Σ+g←A 2Πu transition. A rotational analysis of two bands in this spectrum has been made. The C 2Σ+g state is linear with a C–O bond length of 1.1552(2) Å in the v=0 level. [ABSTRACT FROM AUTHOR]

A technique for the spectroscopic characterization of mass-selected ions in ground and bound excited electronic states involving two-photon absorption and fragment ion detection is demonstrated. A triple quadrupole mass analyzer system is used. Collisionally relaxed ions (M+) from a high pressure source are mass selected, then excited sequentially by two laser colors (λ1,λ2) according to M+→λ1M+*→λ2M+**→F+i and fragment ions (F+i) are detected. Stable ionic states are characterized by scanning λ1 with constant λ2 and this is illustrated on the known transitions of N2O+ (A 2Σ+←X 2Π) and of CS+2 (B 2Σ+u←X 2Πg). New spectroscopic information—vibrational frequencies and rotational constants—and dynamic parameters—lifetimes and fragmentation branching ratios—on N2O+(B 2Σ+) and CS+2 (C 2Σ+g) are obtained by scanning λ2 when λ1 is chosen to populate several or individual rotational levels of the intermediate state. [ABSTRACT FROM AUTHOR]

The electronic spectrum of N2+–He has been measured in the region corresponding to the N2+ B 2Σ+u←X 2Σ+g origin transition. The spectrum was recorded by photoexciting a mass selected beam of N2+–He ions and detecting N2+ fragments. A likely process for the fragmentation involves fluorescence to a vibrationally excited level of the ground electronic state followed by vibrational predissociation. The observed spectrum exhibits well resolved discrete structure and bears a remarkable resemblance to a cold N2+ spectrum suggesting that the potential between the N2+ ion and helium atom in both the X and B electronic states, has at most only a small barrier to internal rotation. Measurement of the shift of N2+–He transitions with respect to the corresponding N2+ lines indicates that the binding energy of the helium atom to the N2+ ion is almost the same in both the B and X electronic states. [ABSTRACT FROM AUTHOR]

A high resolution infrared absorption spectrum of the ionic complex N[sub 2]...Ar[sup +]...N[sub 2] has been observed by tunable diode laser spectroscopy through a supersonic planar plasma. Seventy-six rovibrational transitions were measured involving excitation of the antisymmetric NN (ν[sub 3]) stretching fundamental. The band origin is at 2288.7272(2) cm[sup -1] and the ground state rotational constant is determined as B[sub 0]=0.034 296(7) cm[sup -1]. The spectrum shows a clear spin-statistical intensity alternation and is consistent with a linear and centrosymmetric equilibrium geometry and a ground state with [sup 2]Σ[sub u][sup +] symmetry. The charge is predominantly located on the argon atom. The assignment is supported by high level ab initio calculations carried out. The best estimate for the equilibrium geometry is R[sub e](NN)=1.1014 Å and r[sub e](Ar...N)=2.3602 Å, yielding B[sub e]=0.034 297 cm[sup -1]. The equilibrium dissociation energy D[sub e] for fragmentation into N[sub 2] and [ArN[sub 2]][sup +] is calculated to be ∼1.7 eV. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The diffuse interstellar bands are absorption lines seen towards reddened stars. None of the molecules responsible for these bands have been conclusively identified. Two bands at 9,632 ångströms and 9,577 ångströms were reported in 1994, and were suggested to arise from C60+ molecules (ref. 3), on the basis of the proximity of these wavelengths to the absorption bands of C60+ measured in a neon matrix. Confirmation of this assignment requires the gas-phase spectrum of C60+. Here we report laboratory spectroscopy of C60+ in the gas phase, cooled to 5.8 kelvin. The absorption spectrum has maxima at 9,632.7 ± 0.1 ångströms and 9,577.5 ± 0.1 ångströms, and the full widths at half-maximum of these bands are 2.2 ± 0.2 ångströms and 2.5 ± 0.2 ångströms, respectively. We conclude that we have positively identified the diffuse interstellar bands at 9,632 ångströms and 9,577 ångströms as arising from C60+ in the interstellar medium. [ABSTRACT FROM AUTHOR]