Photodissociation dynamics of $(NO)_2$
The UV photodissociation dynamics of the excited electronic state NO dimer was investigated in the range of 206 nm ~ 222 nm above the threshold of the first open channel, NO(A)+NO(X). The photofragment NO(A) was detected by resonance enhanced multiphoton ionization (REMPI) method and the well distributed rotational spectra of NO(A) were obtained. It shows that the population of the low rotational states is remarkably enhanced as the available energy grows. The energetically accessible three channels of NO(A;ν=0)+NO(X;ν=0), NO(A;ν=0)+NO(X;ν=1), and NO(A;ν=1)+NO(X;ν=0) are considered according to the pump energy. The ratio of the vibrational population of NO(A;ν=0) and NO(A;ν=1) was determined from the spectra and the dissociation barrier height was measured. The statistical calculations of phase space theory (PST) for rotational energy distribution were carried out and separate statistical ensemble (SSE) for vibrational energy distribution was calculated to predict the population distribution and to compare with the experimental data. The Boltzmann plot also shows another cold component and the rotational temperatures were measured. Dynamical factors are needed to understand the photodissociation of $(NO)_2$.
VUV-MATI spectroscopy of DNA/RNA bases
Using vacuum-ultraviolet (VUV) in spectroscopy has many advantages because the excited state does not affect the cationic state. We have just prepared a set-up for generating VUV by using four-wave degenerate mixing of non-linear media such as Kr, Xe, etc. The mass-analyzed threshold ionization (MATI) technique is a crucial method to measure exact ionization potentials and to obtain well resolved low vibrational structures of cations. By combining VUV and MATI, we could measure the IPs and the vibrational structures of biologically very important molecules, thymine and uracil, for the first time. The IPs of thymine and uracil are determined to be 8.9178 ± 0.0010 eV and 9.3411 ± 0.0008 eV, respectively. The structural changes by ionization are not significant and the intense origin peaks are observed in both molecules. The vibrational motions are assigned by comparison with ab initio calculations. Amino acids which do not contain chromophores, other DNA bases and base pairs, and their derivatives are under investigation.
