Abstract
We present a technique for standoff trace chemical sensing that is based on the dependence of excited electronic state lifetimes on the amount of internal vibrational energy. Time resolved photoionization measurements show that the lifetime of the S1 state in N,N-dimethylisopropylamine (DMIPA) decreases exponentially with the amount of energy deposited into vibrational degrees of freedom. This property is employed to acquire spectral signatures of the molecule. Two nanosecond laser pulses are used, one (266 nm) to ionize the molecule through the S1 state and another, with tunable wavelength, to alter the lifetime of the S1 state by depositing energy into vibrations. Reduction of the S1 state lifetime results in a dip in ionization efficiency that is observed by remotely probing the laser-induced plasma with microwave radiation.