Structural and electronic properties of HCnS− (n = 4–11): anion photoelectron spectroscopy and density functional calculations

The structures of HC_nS⁻ are all linear with the H and S atoms locating at two ends of the carbon chain. Their VDEs exhibit a strong odd–even alternation.

Laboratory spectroscopy of astrophysically relevant carbon species

Carbon is one of the most common elements in the solar system, with a fractional abundance of 10(-4) relative to hydrogen. Thus, it is not surprising that over 100 carbon-bearing species have been definitively detected in the interstellar medium via their rotational, infrared, and/or electronic transitions. In order to identify these species, laboratory spectra are needed for comparison to astronomical data. Challenges arise when obtaining laboratory spectra due to the instability of many of these molecules. Over the years, sensitive instrumentation and better techniques for producing these species in situ have been developed to achieve this goal. The use of complementary spectroscopic methods, such as matrix isolation, cavity ringdown, resonance enhanced multiphoton ionization, and ion trapping have led to the identification of several new carbon species at optical and ultraviolet wavelengths. Laboratory spectra have been compared to astronomical data in order to gain further insight into interstellar chemistry. In particular, attempts have been made to identify the carriers of the diffuse interstellar bands, however, with little success. These results are discussed in the following review.

Shedding light on a dark state: the energetically lowest quintet state of C2

In this work we present a deperturbation study of the d (3)Π(g), v=6 state of C(2) by double-resonant four-wave mixing spectroscopy. Accurate line positions of perturbed transitions are unambiguously assigned by intermediate level labeling. In addition, extra lines are accessible by taking advantage of the sensitivity and high dynamic range of the technique. These weak spectral features originate from nearby-lying dark states that gain transition strength through the perturbation process. The deperturbation analysis of the complex spectral region in the (6,5) and (6,4) bands of the Swan system (d(3)Π(g)-a (3)Π(u)) unveils the presence of the energetically lowest high-spin state of C(2) in the vicinity of the d (3)Π(g), v=6 state. The term energy curves of the three spin components of the d state cross the five terms of the 1 (5)Π(g) state at rotational quantum numbers N ≤ 11. The spectral complexity for transitions to the v = 6 level of d (3)Π(g) state is further enhanced by an additional perturbation at N = 19 and 21 owing to the b (3)Σ(g)(-), v=19 state. The spectroscopic characterization of both dark states is accessible by the measurement of 122 "window" levels. A global fit of the positions to a conventional Hamiltonian for a linear diatomic molecule yields accurate molecular constants for the quintet and triplet perturber states for the first time. In addition, parameters for the spin-orbit and L-uncoupling interaction between the electronic levels are determined. The detailed deperturbation study unravels major issues of the so-called high-pressure bands of C(2). The anomalous nonthermal emission initially observed by Fowler in 1910 [Mon. Not. R. Astron. Soc. 70, 484 (1910)] and later observed in numerous experimental environments are rationalized by taking into account "gateway" states, i.e., rotational levels of the d (3)Π(g), v=6 state that exhibit significant (5)Π(g) character through which all population flows from one electronic state to the other.

Rotationally resolved ground state vibrational levels of HC2S studied by two-color resonant four-wave mixing

A high-resolution study of the X(2)Pi(3/2) ground state rovibronic energy levels of jet-cooled HC(2)S radical using the double-resonance two-color four-wave mixing technique (TC-RFWM) is reported. The rotational structure of the bands is observed by excitation of selected R-branch lines in the origin band of the A(2)Pi(3/2)-X(2)Pi(3/2) electronic system. The second laser frequency is scanned to transfer the population from the rotational level(s) of the upper state to selected vibronic levels of the ground state. Fourteen rotationally resolved vibrational bands have been recorded for energies up to 1800 cm(-1) above the v'' = 0 X(2)Pi(3/2) electronic ground state. Effective rotational constants and origins are determined for levels that involve fundamental and overtone combinations of the nu(3) (CS stretch), nu(4) (CCH bend), and nu(5) (CCS bend) vibrations. This illustrates the power and advantages of the TC-RFWM approach for the study of the ground state manifold of reactive intermediates produced in low concentrations with high resolution, good signal-to-noise and wide dynamic range.