Ab initio (MS-CASPT2/cc-pVTZ) potentials of triplet HCCN along the HCC angle. Potential curves were calculated by changing the HCC angle with other geometric parameters relaxed under the restriction of a planar molecule. The HCCN geometry is linear at the HCC angle of 180° for all the five electronic states. The vertical axis denotes the relative energy to the bottom of the ground electronic state.
LIF excitation spectra observed in the discharged jets of (a) CH3CN and (b) CD3CN. The bands indicated by black arrows are the origin bands of the HCCN and DCCN radicals.
High-resolution spectra of the origin bands of (a) HCCN and (b) DCCN. All the assignments are made with the rotational quantum number, N. Transitions originating from the CNC radical are subtracted from the spectrum of DCCN.
Fluorescence temporal profiles observed for the origin band of HCCN/DCCN. (a) Linear scale plots for the temporal profiles of fluorescence decays. Profiles 1–3: HCCN fluorescence emitted from the N = 3(F 2), 2(F 2), 0(F 1) levels, respectively. Profile 4: DCCN fluorescence from the N = 2(F 2) level. (b) Semi-logarithmic plot of the HCCN fluorescence profile emitted from N = 0(F 1). It clearly shows a double-exponential decay with the lifetimes of 15 and 140 ns.
Fluorescence depletion spectra for the origin bands of (a) HCCN and (b) DCCN. Horizontal axis denotes the relative wavenumber to the band origins of HCCN and DCCN, 30 363.27 and 30 353.29 cm−1, respectively. Vertical axis denotes the fluorescence intensity, where the intensity of 100% corresponds to that without fluorescence depletion. The spectra were observed by tuning the fluorescence monitor laser to 30 364.9 cm−1 for HCCN, or 30 354.8 cm−1 for DCCN. Rotational features due to the R 22(2), R 11(1), R 21(1), P 22(2), and P 11(1) transitions are recognized in the spectra.
Stick diagrams of the vibronic bands observed in the fluorescence depletion spectra of (a) HCCN and (b) DCCN. The vertical axis indicates the magnitude of observed depletion (in percent) for the rotational feature of R 22(2) + R 11(1) + R 21(1) without laser power correction. Horizontal axis denotes the relative wavenumber to the band origins of HCCN and DCCN, 30 363.27 and 30 353.29 cm−1, respectively.
Dispersed fluorescence spectrum of HCCN. The spectrum was observed by exciting the molecules through the R-stack of the origin band. Horizontal axis denotes the relative wavenumber to the pump laser frequency, 30 365 cm−1.
Origin band spectra and their rotational simulations (sticks) of (a) HCCN and (b) DCCN. The simulations were made using the molecular constants listed in Table III , assuming the rotational temperature of 6 K. Simulated rotational lines are categorized into three groups based on the spin sub-levels of the upper state.
Ab initio equilibrium geometries and relative electronic energies for the five lowest-lying triplet states of the HCCN radical. a,b
Ab initio harmonic frequencies for the three lowest-lying triplet states of the HCCN radical (in cm−1). a,b
Experimentally determined molecular constants of HCCN and DCCN for the vibronic origin band (in cm−1). a
Band positions in the fluorescence depletion specra of HCCN and DCCN.
Band positions in the dispersed fluorescence spectrum of HCCN.
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