BEHAVIOR OF POLYATOMIC-MOLECULES IN INTENSE INFRARED-LASER BEAMS

In the present Letter we report that a number of polyatomic molecules (M) when irradiated with short pulse lasers <90 fs at 750-790 nm and i ntensities up to 10(15) W cm(-2) produce multiply charged parent ions and do not fragment to any great degree. This surprising observation i s found in both linear and ring structured molecules and is very simil ar to the behavior of inert atoms such as xenon under the same irradia tion condition. This is a very different behavior from irradiating wit h nanosecond pulses at 10(9) W cm(-2) where low-mass fragments dominat e the spectrum. For the hydrocarbon molecules presented in this work, there exists an envelope of 2(+) ionized peaks, which corresponds to t he parent and a number of (M - nH) satellites. This feature is charact eristic of these molecules in the intensity region 10(14-15) W cm(-2) and is interpreted as evidence for tunneling or barrier suppression. C oulomb explosion leading to multiply charged atoms, which is evident f or CS2, does not seem to be operating for the larger hydrocarbon molec ules.