Catching polyatomic ions
doi:10.1038/nindia.2012.78 Published online 21 May 2012
A polyatomic ion that was thus far inaccessible with conventional mass spectroscopy has now been uncovered using extremely short laser pulses. Catching a glimpse of this ion would open up new possibilities in modifying molecular surfaces in a wide range of chemical reactions.
Using lasers to image and control complex chemical reactions remains an intense pursuit of contemporary molecular physics. Most of today's studies focus on small molecules like hydrogen. Conventional mass spectrometry of symmetrical molecules such as tetramethylsilane (TMS) doesn't provide information on its constituent ions.
To catch a glimpse of the polyatomic ions of TMS, the researchers exposed TMS to both short and long pulses of the same intensity. The results showed that measurements made with 100 femtosecond (fs) and 200 fs pulses yielded no evidence of the TMS ion molecular peak, which is consistent with the results of conventional mass spectrometry. However, the TMS ion made an appearance when a 22 fs pulse was used, and persisted when 5 fs pulses were used.
The researchers observed bond hardening with both the 5 fs (two-cycle) and 22 fs (eight-cycle) pulses. Bond hardening disappeared when longer pulses (>100 fs) of the same intensity were used. It was during this bond-hardening process that the TMS ions appeared. This observation contradicts Jahn–Teller effect theory, which says that the TMS ion is unstable.
The findings of this research are significant because TMS is used as an aviation fuel and has many potential uses in the photonics industry. The researchers say that the results are important from the viewpoint of optically generating polyatomic molecular ions that are normally inaccessible.
The authors of this research are from: Tata Institute of Fundamental Research, Mumbai, and Indian Institute of Science Education and Research Kolkata, Mohanpur, India.