On the competition between photoionisation and photodissociation of molecular deuterium after (3+1) resonance-enhanced multiphoton excitation via theB-1 Sigma(+)(u) state

We present a (3+1) one-colour resonance-enhanced multiphoton ionisation stu dy employing kinetic-energy resolved photoelectron detection via the (nu' = 10-13, N' =0-3) levels of the B(1)Sigma(u)(+)(1s sigma(g))(2p sigma(u)) st ate of molecular deuterium. when the four-photon energy is below the D(n=1) +D(n=3) energy threshold a competition between molecular photoionisation an d photodissociation is observed. In the dissociation process excited D atom s are generated which are subsequently ionised after absorption of one addi tional photon. In the energy region studied above the D(n=1)+D(n=3) thresho ld the prevailing exit channel is photodissociation with the formation of D (n=3). These results provide further evidence that the vibrational continua of singly excited (1s sigma(g))(nl lambda) Rydberg states play a crucial r ole in the photodissociation process; (C) 2000 Elsevier Science B.V. All ri ghts reserved.