Fig. 1. Vibrational levels in different excited states of NH₃ and NH3+ without the existence of ponderomotive force potential. Single arrow represents the energy of a photon, and double arrow refers to the detected kinetic energy (KE) of electrons.

Fig. 2. Photoelectron images of NH₃ molecules. The laser wavelength is 400 nm, and the intensity range is 1.01 × 10¹³ W/cm²–1.01 × 10¹⁴ W/cm². (a)–(n) Corresponding photoelectron distribution images with the laser intensity of 1.01, 1.27, 1.52, 1.90, 2.53, 3.17, 3.80, 4.43, 5.07, 5.70, 6.30, 7.60, 8.87, 10.10 × (10¹³ W/cm²). Horizontal and vertical coordinates are x and y pixels of CCD, respectively, and the direction of laser polarization is represented by arrows.

Fig. 3. Kinetic energy distributions from slow electrons within the range of 0 eV–3.1 eV with laser intensities being 1.0, 1.27, 1.52, 1.90, 2.53, 3.17, 3.80, 4.43, 5.07, 5.70, 6.30, 7.60, 8.87, and 10.1 × (10¹³ W/cm²).

Fig. 4. Kinetic energy distributions of fast electrons within the range of 3.1 eV–10 eV with laser intensities being 1.01, 1.27, 1.52, 1.90, 2.53, 3.17, 3.80, 4.43, 5.07, 5.70, 6.30, 7.60, 8.87, and 10.1 × (10¹³ W/cm²).

Fig. 5. Angular distributions of peaks 1, 2, 3, and 4, corresponding to 1.01 × 10¹³ W/cm² laser intensity.

Fig. 6. Angular distributions of peak 4 at different laser intensities.

Fig. 7. Angular distribution of peak 5 at laser intensity 5.07 × 10¹³ W/cm².

Fig. 8. Angular distribution of peaks 4, 5, and 6 at the 5.07 × 10¹³-W/cm² laser intensity.

Fig. 9. Results and identification for multi-photon processes of ammonia in the 400-nm wavelength laser field. Colored arrows in this picture illustrate different multi-photon processes; all photons have the 400-nm wavelength.

Table 1. In non-ponderomotive force case, values of energy needed for ammonia molecule to transform from the X^∼ state to different vibration levels of (upper) A state and (lower) ammonia ion.