Relaxation of highly vibrationally excited pyrimidine (C(4)N(2)H(4)) by collisions with carbon dioxide has been investigated using diode laser transient absorption spectroscopy. Vibrationally hot pyrimidine (E(')=40 635 cm(-1)) was prepared by 248-nm excimer laser excitation, followed by rapid radiationless relaxation to the ground electronic state. The nascent rotational population distribution (J=58-80) of the 00(0)0 ground state of CO(2) resulting from collisions with hot pyrimidine was probed at short times following the excimer laser pulse. Doppler spectroscopy was used to measure the CO(2) recoil velocity distribution for J=58-80 of the 00(0)0 state. Rate constants and probabilities for collisions populating these CO(2) rotational states were determined. The measured energy transfer probabilities, indexed by final bath state, were resorted as a function of DeltaE to create the energy transfer distribution function, P(E,E(')), from E(')-E approximately 1300-7000 cm(-1). P(E,E(')) is fitted to a single exponential and a biexponential function to determine the average energy transferred in a single collision between pyrimidine and CO(2) and parameters that can be compared to previously studied systems using this technique, pyrazineCO(2), C(6)F(6)CO(2), and methylpyrazineCO(2). P(E,E(')) parameters for these four systems are also compared to various molecular properties of the donor molecules. Finally, P(E,E(')) is analyzed in the context of two models, one which suggests that the shape of P(E,E(')) is primarily determined by the low-frequency out-of-plane donor vibrational modes and one which suggests that the shape of P(E,E(')) can be determined by how the donor molecule final density of states changes with DeltaE.

We show experimentally that spectral phase manipulation of ultrashort extreme-uv light pulses can induce and control coherent transient excitation of the He͑1s3p͒ excited state by the nonresonant components of the broadband extreme-ultraviolet light. The spectral phase manipulation of the 15th harmonic of an intense 805 nm, 80 fs pulse is achieved by propagation of the euv light through a variable optical density of He gas. The acquired spectral phase due to the dispersive interaction of the off-resonance components in the euv pulse with the He͑1s3p͒ resonance enhances and modifies the transient excitation. The temporal evolution of the coherently prepared transient He͑1s3p͒ amplitude is probed by ionization to the continuum with a 400 nm, 80 fs pulse.