Plumbane

Plumbane, PbH₄, is a metal hydride composed of lead and hydrogen. Plumbane is not well-characterized or well-known, and it is thermodynamically unstable with respect to the loss of a hydrogen atom. Derivatives of plumbane include lead tetrafluoride, (PbF₄), and tetraethyllead, ((CH₃CH₂)₄Pb).

History

Until recently, it was uncertain whether plumbane had ever actually been synthesized; although, the first reports date back to the 1920s and in 1963, Saalfeld and Svec reported the observation of PbH+
4 by mass spectrometry. Plumbane has repeatedly been the subject of Dirac–Hartree–Fock relativistic calculation studies, which investigate the stabilities, geometries, and relative energies of hydrides of the formula MH₄ or MH₂.

Properties

Plumbane is an unstable colorless gas and is the heaviest group IV hydride. Furthermore, plumbane has a tetrahedral (T_d) structure with an equilibrium distance between lead and hydrogen of 1.73 Å. By weight percent, the composition of plumbane is 1.91% hydrogen and 98.09% lead. In plumbane, the formal oxidation states of hydrogen and lead are -1 and +4, respectively, because the electronegativity of hydrogen is higher than that of lead. The stability of metal hydrides with the formula MH₄ (M = C–Pb) decreases as the atomic number of M increases.

Paro Airport

Paro Airport (IATA: PBH, ICAO: VQPR) is the sole international airport in Bhutan. The airport is located 6 km (3.7 mi; 3.2 nmi) from Paro in a deep valley on the bank of the river Paro Chhu. With surrounding peaks as high as 5,500 m (18,000 ft) it is considered one of the world's most challenging airports. As of October 2009, only eight pilots in the world were certified to land at the airport. Flights at Paro are allowed under visual meteorological conditions only and are restricted to daylight hours from sunrise to sunset. It is one of only four airports in Bhutan.

History

In 1968, the Indian Border Roads Organisation built an airstrip in the Paro valley, which was initially utilised for on call helicopter operations by the Indian Armed Forces on behalf of Royal Government of Bhutan. Bhutan's first airline, Drukair, was established by Royal Charter on 5 April 1981.

Paro Airport is located deep in a valley 2,235 m (7,332 ft) above mean sea level and is surrounded by mountains as high as 5,500 m (18,000 ft). Initially, the airport was constructed with a runway 1,200 m (3,900 ft) in length, giving the Bhutanese government specific requirements for a choice of aircraft to be operated from Paro. They required an 18–20 seat STOL-capable aircraft with operating capabilities which included a high service ceiling, high rate of climb and high manoeuvrability. The major requirement for the aircraft was that it must be capable of flying Kolkata – Paro – Kolkata, a 1,200 km (750 mi; 650 nmi) round-trip, without refuelling; due to minimal infrastructure being available at Paro for this purpose. Three different aircraft types were considered after flight tests that had been conducted in India and Bhutan between 1978 and 1980; however, none was deemed suitable.