Does (Ser)2 have a neutral structure? How does the zwitterion evolve with an increasing cluster size of serine (Ser)? Infrared spectroscopic and mass‐spectrometric analysis of [H(Ser)n]+ (n=2–8) shows progressive stabilization of the zwitterion with increasing cluster size, and the results of ab initio calculations based on density functional theory of [H(Ser)2]+ are also given (picture: a neutral structure; red O, blue N, gray C, white H).

Vacuum ultraviolet ͑VUV͒ laser photoionization is combined with time-of-flight ͑TOF͒ mass spectrometry to determine the photofragments produced from the laser photodissociation of allene and propyne in a molecular beam. Detection of C 3 H 3 ϩ confirms that atomic hydrogen elimination is the primary process for both of these molecules. A hydrogen molecule elimination channel and a low mass carbon fragmentation channel of allene to produce C 3 H 2 ϩH 2 and CH 2 ϩC 2 H 2 , respectively, have also been identified. Different ratios of various dissociation channels from these two molecules suggest that the dissociation mechanisms of these two isomers are different. Dissociation must occur before complete isomerization. These results are discussed in terms of recent theoretical calculations on the ground and excited states of these molecules. Secondary photodissociation of the products has been observed, even though the laser energies that have been used are less than 8 mJ/cm 2 and the photolysis laser is not focused. Therefore, the present results show how important it is to determine product distributions as a function of the laser energy.

Synchrotron radiation is used to excite Ar to the intermediate states 3p 1/2 5 ͑3dЈ͓3 / 2͔ 1 , 5dЈ͓3 / 2͔ 1 , 5sЈ͓1 / 2͔ 1 , 7sЈ͓1 / 2͔ 1 ͒ and 3p 3/2 5 ͑6d͓1 / 2͔ 1 , 6d͓3 / 2͔ 1 , 8s͓3 / 2͔ 1 ͒, then excited by lasers to the autoionizing Rydberg series 3p 1/2 5 npЈ ͓͑1 / 2͔ 0,1 , ͓3 / 2͔ 1,2 ͒ and nfЈ͓5 / 2͔ 2. For the intermediate states of 5sЈ, 7sЈ, and 8s, the npЈ ͓͑1 / 2͔ 0 and ͓3 / 2͔ 2 ͒ series are observed with high intensity but not the npЈ ͓͑1 / 2͔ 1 and ͓3 / 2͔ 1 ͒ series when the polarization vectors of two light beams are in parallel; but when they are in orthogonal, the npЈ͓1 / 2͔ 0 series disappears, the npЈ͓3 / 2͔ 2 intensity remains, and the npЈ ͓͑1 / 2͔ 1 and ͓3 / 2͔ 1 ͒ series show up strongly. The intensity distribution of the npЈ series strongly depends on the intermediate state. The spectra of the npЈ series are assigned according to their intensity variation with the polarization vectors. The quantum defects determined for the series npЈ͓1 / 2͔ 0 ͑n =11-57͒, npЈ͓3 / 2͔ 2 ͑n =11-65͒, npЈ͓3 / 2͔ 1 ͑n =11-31͒, and nfЈ͓5 / 2͔ 2 ͑n =9-74͒ are 1.611Ϯ 0.011, 1.683Ϯ 0.013, 1.688Ϯ 0.010, and 0.016Ϯ 0.005, respectively. Our values are in excellent agreement with theoretical prediction. The spectral line shapes of autoionizing Rydberg states are analyzed with a Beutler-Fano profile. Reduced autoionization linewidths for the npЈ͓1 / 2͔ 0 ͑n =11-16͒ series vary in the range 2549-4145 cm −1 , and the nfЈ͓5 / 2͔ 2 ͑n =9-11͒ series in 186-247 cm −1 in reasonable agreement with theoretical prediction.