No abstract

Strong-field laser–molecule interaction forms much of the basis for initiating and probing ultrafast quantum dynamics. Previous studies aimed at elucidating the origins of vibrational coherences induced by intense laser fields have been confined to diatomic molecules. Furthermore, in all cases examined to date, vibrational wave packet motion is found to be induced by R-selective depletion; wave packet motion launched by bond softening, though theoretically predicted, remains hitherto unobserved. Here we employ the exquisite sensitivity of femtosecond extreme ultraviolet absorption spectroscopy to sub-picometer structural changes to observe both bond softening-induced vibrational wave packets, launched by the interaction of intense laser pulses with iodomethane, as well as multimode vibrational motion of the parent ion produced by strong-field ionization. In addition, we show that signatures of coherent vibrational motion in the time-dependent extreme ultraviolet absorption spectra directly furnish vibronic coupling strengths involving core-level transitions, from which geometrical parameters of transient core-excited states are extracted.

The eastern Tibetan Plateau has become increasingly warmer and drier since the 1990s. Such warming and drying has a great impact on ecosystem processes on the eastern Tibetan Plateau. To determine their combined effects on CO 2 and N 2 O emission rates, we conducted a field manipulative experiment in an alpine meadow of the eastern Tibetan Plateau during the growing season of 2009. The experiment showed that warming manipulation increased soil temperature by 1°C, and drying manipulation decreased soil water content by 6.8 %. We found that by counteracting the effect of low temperature in the area, experimental warming significantly increased soil microbial biomass, the number of bacteria, fungi, actinomycetes, ammonifying bacteria, nitrobacteria and denitrifying bacteria, and facilitated the emission rates of CO 2 and N 2 O by 33.4 and 31.5 %, respectively. However, decreased precipitation further aggravated soil water stress and inhibited the numbers of these organisms, and reduced the emission rates of CO 2 and N 2 O by 47.4 and 37.9 %, respectively. So decreased soil water content tended to offset the positive effect of warming. Compared to the positive effects of warming, decreased soil water content was shown in our study to have even greater impact on the eastern Tibetan Plateau during the growing season. Therefore, inhibition of CO 2 and N 2 O emission rates (32.3 and 29.3 %, respectively) by warming and drying will intensify if the combined effects of these climatic trends persist in the region.