Probed by Liquid Jet Time-Resolved Photoelectron Spectroscopy. ChemRxiv. Preprint. The relaxation dynamics of thymine and its derivatives thymidine and thymidine monophosphate were studied using time-resolved photoelectron spectroscopy applied to a water microjet. Two absorption bands were studied, the first is a bright ππ* state which was populated using tunable-ultraviolet light in the range of 4.74-5.17 eV and probed using a 6.20 eV probe pulse. By reversing the order of these pulses, a band containing multiple ππ* states was populated by the 6.20 eV pulse and the lower energy pulse served as the probe. The lower lying ππ* state was found to decay in ~400 fs in both thymine and thymidine independent of pump photon energy while thymidine monophosphate decays varied from 670-840 fs with some pump energy dependence. The application of a computational QM/MM scheme at the XMS-CASPT2//CASSCF/AMBER level of theory suggests that conformational differences existing between thymidine and thymidine monophosphate in solution accounts for this difference. The higher lying ππ* band was found to decay in ~600 fs in all three cases, but was only able to be characterized when using the 5.17 eV probe pulse. Notably, no long-lived signal from an np* state could be identified in either experiment on any of the three molecules. File list (3) download file view on ChemRxiv Thymine_to_submit.docx (1.52 MiB) download file view on ChemRxiv SI_to_submit.docx (894.21 KiB) download file view on ChemRxiv Thymine_to_submit.pdf (1.40 MiB)

The excited state relaxation dynamics of adenosine and adenosine monophosphate were studied at multiple excitation energies using femtosecond time-resolved photoelectron spectroscopy in a liquid water microjet. At pump energies of 4.69-4.97 eV, the lowest ππ * excited state, S 1 , was accessed and its decay dynamics were probed via ionization at 6.20 eV. By reversing the role of the pump and probe lasers, a higher-lying ππ * state was excited at 6.20 eV and its time-evolving photoelectron spectrum was monitored at probe energies of 4.69-4.97 eV. The S 1 ππ * excited state was found to decay with a lifetime ranging from ∼210 to 250 fs in adenosine and ∼220 to 250 fs in adenosine monophosphate. This lifetime drops with increasing pump photon energy. Signal from the higherlying ππ * excited state decayed on a time scale of ∼320 fs and was measureable only in adenosine monophosphate.

<p>The relaxation dynamics of thymine and its derivatives thymidine and thymidine monophosphate were studied using time-resolved photoelectron spectroscopy applied to a water microjet. Two absorption bands were studied, the first is a bright ππ* state which was populated using tunable-ultraviolet light in the range of 4.74 – 5.17 eV and probed using a 6.20 eV probe pulse. By reversing the order of these pulses, a band containing multiple ππ* states was populated by the 6.20 eV pulse and the lower energy pulse served as the probe. The lower lying ππ* state was found to decay in ~400 fs in both thymine and thymidine independent of pump photon energy while thymidine monophosphate decays varied from 670-840 fs with some pump energy dependence. </p><p>The application of a computational QM/MM scheme at the XMS-CASPT2//CASSCF/AMBER level of theory suggests that conformational differences existing between thymidine and thymidine monophosphate in solution accounts for this difference. The higher lying ππ* band was found to decay in ~600 fs in all three cases, but was only able to be characterized when using the 5.17 eV probe pulse. Notably, no long-lived signal from an np* state could be identified in either experiment on any of the three molecules.</p>

Perdeutero-spiropentane (C 5 D 8) has been synthesized, and infrared and Raman spectra are reported for the first time. Wavenumber assignments are made for most of the fundamental vibrational states. Gas phase infrared spectra were recorded at a resolution (0.002 cm-1) sufficient to resolve individual rovibrational lines and show evidence of strong Coriolis and/or Fermi resonance interactions for most bands. However a detailed rovibrational analysis of the fundamental ν 15 (b 2) parallel band proved possible, and a fit of more than 1600 lines yielded a band origin of 1053.84465(10) cm-1 and ground state constants (in units of cm-1): B 0 = 0.1120700(9), D J = 1.51(3) x10-8 , D JK = 3.42(15) x10-8. We note that the B 0 value is significantly less than a value of B a = 0.1140 cm-1 calculated using structural parameters from an earlier electron diffraction (ED) study, whereas one expects B a to be lower than B 0 because of thermal averaging over higher vibrational levels. A similar discrepancy was noted in an earlier study of C 5 H 8 [1]. The structural and spectroscopic results are in good accord with values computed at the anharmonic level using the B3LYP density functional method with a cc-pVTZ basis set.

Gas-phase electron-diffraction (GED) data have been combined with recent spectroscopic rotational constants to determine the r structural parameters for spiropentane, CH. The structure has D symmetry, and the results yield values of 1.105(2) Å for the CH bond length, 1.557(3) Å for the distal CC bond length, and a smaller value of 1.482(1) Å for the four lateral CC bonds that connect to the central carbon atom. The HCH angle is 113.7(13)°, and the HCH flap angle, defined as the angle of the HCH bisector and the distal CC bond, is 150.2(16)°. Corresponding r values are 1.122(2) Å, 1.560(3) Å, 1.485(1) Å, 115.1(13)°, and 148.9 (16)°. The results are in good accord with values from density functional calculations (B3LYP/cc-pVTZ) and resolve some questions about the structure reported in an earlier GED study, in particular about the HCH angle and anomalous rotational constants calculated for the structure.