Shiki Shigetomo, Ukibe Masahiro, Sato Yuki, Tomita Shigeo, Hayakawa Shigeo, Ohkubo Masataka
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, 305-8568, Japan.
J Mass Spectrom. 2008 Dec;43(12):1686-91. doi: 10.1002/jms.1459.
A double-focusing mass spectrometer (MS) equipped with a superconducting-tunnel-junction (STJ) detector has been applied to measure relative ionization cross-sections for the production of ions that are accompanied by different ion species with the same mass-to-charge (m/z) value. The STJ detector fabricated for this study enables kinetic energy (E) measurement of incoming individual ions at a counting rate of up to approximately 100 k ions/s and an energy resolution (DeltaE/E) of 15%. Both high counting rate and high-energy resolution are necessary to independently determine both m and z and not the m/z value only in ion-counting MS experiments. Ions such as (14)N(2) (2+) and (14)N(+) with the same m/z value can be clearly discriminated using a kinetic-energy-sensitive MS. This fine discrimination capability allows direct determination of relative ionization cross-sections of the homonuclear diatomic ions (14)N(2) (2+)/(14)N(2) (+) and (16)O(2) (2+)/(16)O(2) (+), which are difficult to measure due to the strong interference by the signals of their dissociated atomic ions with noticeably large ionization cross-sections. The new instrument requires no low-abundance heteronuclear diatomic molecules of the forms (14)N(15)N or (16)O(17)O to carry out ionization studies and thus, is expected to be useful in fields such as atmospheric science, interstellar science, or plasma physics.
一台配备超导隧道结（STJ）探测器的双聚焦质谱仪（MS）已被用于测量产生离子时的相对电离截面，这些离子伴随着具有相同质荷比（m/z）值的不同离子种类。为本研究制造的STJ探测器能够以高达约100 k离子/秒的计数率和15%的能量分辨率（ΔE/E）测量入射单个离子的动能（E）。在离子计数质谱实验中，高计数率和高能量分辨率对于独立确定m和z而非仅确定m/z值都是必要的。使用动能敏感质谱仪可以清晰地区分具有相同m/z值的离子，如（14）N₂（2⁺）和（14）N⁺。这种精细的区分能力使得能够直接测定同核双原子离子（14）N₂（2⁺）/（14）N₂（⁺）和（16）O₂（2⁺）/（16）O₂（⁺）的相对电离截面，由于它们离解的原子离子信号具有明显大的电离截面而产生强烈干扰，这些相对电离截面难以测量。新仪器在进行电离研究时不需要低丰度的（14）N（15）N或（16）O（17）O形式的异核双原子分子，因此有望在大气科学、星际科学或等离子体物理等领域发挥作用。
