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Damage by late spring frost is a risk deciduous trees have to cope with in order to optimize the length of their growing season. The timing of spring phenological development plays a crucial role, not only at the species level, but also at the population and individual level, since fresh new leaves are especially vulnerable. For the pronounced late spring frost in May 2011 in Germany, we studied the individual leaf development of 35 deciduous trees (mainly European beech Fagus sylvatica L.) at a mountainous forest site in the Bayerischer Wald National Park using repeated digital photographs. Analyses of the time series of greenness by a novel Bayesian multiple change point approach mostly revealed five change points which almost perfectly matched the expected break points in leaf development: (i) start of the first greening between day of the year (DOY) 108–119 (mean 113), (ii) end of greening, and (iii) visible frost damage after the frost on the night of May 3rd/4th (DOY 123/124), (iv) re-sprouting 19–38 days after the frost, and (v) full maturity around DOY 178 (166–184) when all beech crowns had fully recovered. Since frost damage was nearly 100%, individual susceptibility did not depend on the timing of first spring leaf unfolding. However, we could identify significant patterns in fitness linked to an earlier start of leaf unfolding. Those individuals that had an earlier start of greening during the first flushing period had a shorter period of recovery and started the second greening earlier. Thus, phenological timing triggered the speed of recovery from such an extreme event. The maximum greenness achieved, however, did not vary with leaf unfolding dates. Two mountain ashes (Sorbus aucuparia L.) were not affected by the low temperatures of -5°C. Time series analysis of webcam pictures can thus improve process-based knowledge and provide valuable insights into the link between phenological variation, late spring frost damage, and recovery within one stand.

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The nature of the intermolecular bonding in the indole-water complex is investigated by highly resolved UV-REMPI spectra with rotational fine structure. First, we determine the coordinates of the amino hydrogen atom by isotope substituting it with deuterium for the S 0 electronic ground and S 1 excited state of indole. In a second step, we calculate the rotational fine structure resulting from possible cluster structures and compare it with the experimental results. A fit routine adapts the spectroscopic constants within the condition of a planar complex which is a reasonable assumption for the observed rotational a,b-type band structure. The best agreement between simulation and experiment is found when the water molecule oxygen is located 2.93(5) Å away from the amino hydrogen of indole. This clearly demonstrates that in the indole-water complex a hydrogen bond is formed between the hydrogen donor indole and the oxygen atom of the water molecule. Upon electronic excitation to S 1 this bond length is nearly constant.

High resolution ultraviolet (UV) and molecular beam Fourier transform microwave (MB FTMW) spectroscopy of the benzonitrile-water (BZNW) cluster were performed to measure cluster structures in the So and Si states. The MW experiments provide additional information on the structure and the 14 N-nuclear quadrupole coupling in the ground state So, the UV experiments on the dynamics in Si.The rotationally resolved sub-Doppler UV spectra of BZNW were measured by mass-selective resonance-enhanced two-photon ionization. For the first time this UV technique has been applied to hydrogen-bonded clusters. From the UV spectra the rotational constants are obtained by Correlation Automated Rotational Fitting. The MW spectra were analyzed with the model of a centrifugally distorted rotor including nuclear quadrupole coupling. A r 0 -fit of the water position within the cluster is performed. The water is found to be located with its oxygen nearly in the plane of benzonitrile (BZN). For So (Si), the distance of the oxygen to the ortho hydrogen is r 0 = 2.477(4) Ä (2.457(2) A) and the angle to the ortho carbon-hydrogen bond 143.34(2)° (141.91(3)°). The structure differences in Si and So can be explained by the structure changes of the BZN molecule. A line broadening, which points to a faster decay in Si upon clustering with the polar solvent, is observed for the BZNW cluster.

Highly resolved (Δν<100 MHz) UV-REMPI (ultraviolet-resonantly enhanced multiphoton ionization) spectra of different vibronic bands in the phenol–water complex are presented. The torsional splitting caused by the hindered rotation of the water moiety in the hydrogen-bonded system is investigated. An autocorrelation procedure reveals torsional subbands, a correlation automated rotational fitting (CARF) of the spectra yields the rotational constants: The analyzed vibrations are classified by the rotational constants of the corresponding vibronic band and the symmetry of the torsional state. The transition to the stretching vibration at 156 cm−1 excess energy is shown to consist of two different torsional transitions similar to the electronic origin. The torsional splitting in the origin band is 0.8491(2) cm−1 and that of the stretching vibration is 0.8915(3) cm−1, demonstrating a very small coupling between the stretching and the torsional motion. We assign the 121 cm−1 band as the negative parity component of the transition to the wagging vibration β2 while the band at 125 cm−1 is tentatively assigned as the positive parity component of the same band. The resulting large torsional splitting of −4.596(3) cm−1 points to a strong coupling to the torsional motion. The band at 95 cm−1 has only one torsional parity component within its rotational envelope. The observed large change of its rotational constants does not fit to the pattern of the other vibrations and the band is tentatively assigned as an overtone of the torsional vibration τ with positive parity.

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